SMS glossary

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The glossary below defines common terms and acronyms in the SMS industry. 


A2P: Application-to-Person (A2P) messaging is any kind of message traffic in which a person receives messages from an application rather than another individual, and when it is typically not expected to receive a reply. A2P message includes, but is not limited to, marketing communications, appointment reminders, chat bots, notifications, and one-time passwords (OTPs) or PIN codes.

Aggregator: an SMS aggregator is a link between carriers and software. They build and maintain the technical relationships with wireless carriers. An aggregator is a third-party who connects via the Short Message Peer-to-Peer (SMPP) directly to the wireless service provider in order to offer services to consumers on behalf of content providers. 

Alphanumeric sender ID: see Branded sender ID.

ASP: stands for application service provider. An organization that offers network based software solutions (i.e., applications) or downloadable applications that enable the business logic behind mobile marketing initiatives. 

ATDS: stands for automatic telephone dialing system. To qualify as an ATDS under the TCPA, a device must have the capacity either to store a telephone number using a random or sequential number generator, or to produce a telephone number using a random or sequential number generator. (Facebook, Inc. v. Duguid. April 1 2021:

Audit notice: report issued to noncompliant short code programs detailing the specific violations and actions required to bring the program into compliance.


Branded sender ID: a type of SMS sending number used in the UK and Australia; it cannot send MMS messages or receive any text messages. The sender ID can be customized to match your brand. 


Carrier: also referred to as a mobile or wireless carrier. Carriers provide cellular services, allowing phones and tablets to connect with each other. AT&T, T-Mobile, and Verizon are all wireless carriers.

CASL: stands for Canadian Anti-Spam Legislation. Read about CASL

Clicked SMS: metric for when a recipient clicks on a link within an SMS message.

Consented to Receive SMS: metric for when a recipient confirms that they want to receive your messages.

Conversational message: conversational messaging is a back-and-forth conversation that takes place via text. 

CSCA: stands for common short code administration. Also known as the short code registry 

CTA: stands for call-to-action. Language encouraging or inviting a consumer to opt in and consent to receive SMS/MMS text messages. Typically an online signup form, click-to-text, or text-to-join email or website banner.

CTIA: stands for Cellular Telecommunications Industry Association. The CTIA is a trade organization run by wireless companies such as AT&T, Verizon, etc. It established the short code system and provided guidelines against SHAFT (see entry below).

Custom keyword: a type of keyword that you create in Klaviyo to allow customers to subscribe to your SMS marketing efforts. Custom keywords must be between 3 and 20 characters and only include alphanumeric characters. They cannot be words that people commonly use in normal text conversations (e.g., is, are, can, will, his, there, why, the, about, etc.) or that pertain to SHAFT or illegal activities (e.g., CBD). 

CWTA: stands for Canadian Wireless Telecom Association. Canadian wireless authority that owns National short code. 


Destination number: a destination number is the phone number that receives an SMS/MMS. When you send an SMS, your customers phone number would be a destination number. When your customer sends an SMS to you (see sent SMS) your phone number would be the destination number. 


Express consent: also called explicit consent. Express/explicit consent occurs when someone directly tells you that they want to receive marketing messages from your brand. Express consent is required to send SMS messages using Klaviyo. 

E.164: a phone number format. E.164 defines a general format for international telephone numbers. Numbers are limited to a maximum of 15 digits, excluding the international call prefix. E.164 is one of several accepted phone number formats for SMS in Klaviyo. See also E.123, RFC3966.

E.123 International: a phone number format. Examples are +12 345 678 900 and +1 234 567 8900.

E.123 National: a phone number format. Examples are 1234) 567 8900 and 12345678900.


Failed to Deliver SMS: metric for when a message is sent but not delivered to the recipient.

FCC: stands for Federal Communications Commision. US federal agency responsible for implementing and enforcing America’s communications law and regulations. 

Filtering: when a message is not delivered by a wireless carrier. Wireless carriers filter SMS and MMS messages they believe may be spam or do not meet content requirements (e.g., includes terms related to SHAFT or CBD).


Handset opt-in: recipients can opt into a short code by sending a text message or opting in from a mobile app (handset opt-in), as opposed to non-handset opt-in. These designations are important for Canadian short codes.


ICV: stands for inter-carrier vendor. Also called “hub providers,” ICVs act as hubs to facilitate interoperability by transporting messaging traffic between multiple wireless providers and cloud-based providers.

Implied consent: also called implicit or inferred consent. Implied consent is when someone gives you their contact information (e.g., phone number), but does not explicitly say they want to receive marketing messages from your brand. 

Informational message: informational messaging is when a consumer gives their phone number to a business and asks to be contacted in the future. Appointment reminders, welcome texts, order updates, and alerts typically fall into this category.

ISV: stands for independent software vendor.


Keyword: also known as just keyword response. These are words that, when sent by a subscriber, prompt a certain action and an automated response. For instance, if a subscriber texts “STOP,” they will automatically be unsubscribed from receiving SMS from your brand and a message will go out informing them of this action. Other examples of keywords are HELP, INFO, CANCEL, and QUIT. Keywords are not case-sensitive.


Long code: also called a long number. It is a type of SMS and MMS sending number consisting of 10 digits and looks like a regular phone number (1-XXX-XXX-XXXX). 


MIN: stands for mobile identification number, more commonly referred to as a wireless phone number which uniquely identifies a wireless device within a WSP’s network.

Mini-TCPA: Florida’s telemarketing rules. Essentially a stricter version of the federal Telephone Consumer Protection Act (TCPA). The law, CS/SB 1120, known as Florida’s "Mini-TCPA," puts tighter boundaries on who you can send to and when, as well as how many messages a recipient can receive in a certain timeframe.

MMS: stands for multimedia message service. This is a type of text message that includes multimedia, such as an image or GIF.

MO: stands for mobile originating, which is a message that is sent by the consumer. 

MT: stands for mobile terminating, which is a message sent to the consumer.


NANP: stands for North American numbering plan. The NANP is a telephone numbering plan for 25 regions in 20 countries, primarily in North America and the Caribbean. The NANP divides the territories of its members into numbering plan areas (NPAs), which are encoded numerically with a 3-digit telephone number prefix, commonly called the area code and a 7-digit local number.

Network security vendors: network security vendors provide solutions that enable wireless providers, cloud-based providers, and ICVs to identify unwanted messaging traffic. These solutions deliver a variety of network security features, including spam containment and management.

Non-handset opt-in: recipients can opt into a short code by signing up on a website, filling out a paper form, making a verbal agreement, or otherwise opting in without using a handset, as opposed to handset opt-in. These designations are important for Canadian Short Codes.

NPA: stands for numbering plan area. A 3-digit numbering code, commonly called an area code.


P2P: stands for person-to-person messaging. This is when 2 or more people communicate over text messaging. For example, when you send a text message from your phone to another person's phone, that's P2P. Under some circumstances, this may also include traffic that goes through an API to connect 2 people; however, some countries (including the US and Canada) do not consider any application-mediated traffic to be P2P.

PECR: stands for public and electronic communication regulations, a UK law that implements the EU’s ePrivacy directive (directive 2002/58/EC) and sets out privacy rights relating to electronic communications. 

Porting: transferring an existing phone number from one service provider to another. 

Program: a program proposed by a content provider relating to the use of a common short code; e.g., promotional (marketing), transactional (alerts, updates, etc.), and sweepstakes (contests, text-2-win campaigns). 

Promotional message: promotional messaging is a message sent that contains a sales or marketing promotion. Adding a call-to-action (e.g., a coupon code to an informational text) may place the message in the promotional category. Before a business sends promotional messages, the consumer should agree in writing to receive promotional texts.


Received SMS: metric for when Klaviyo has recorded that your recipient has received an SMS.

RFC3966: a phone number format. The RFC3966 format is a URI that comprises the prefix “tel:” followed by numbers (ex. tel: 12345678900).


SCC: stands for short code council (Canada). A committee within the CWTA comprised of one voting representative from each of the participating WSP.

Sent SMS: Klaviyo metric for when someone texted your destination number. This metric is logged for any inbound message sent from your subscribers to your destination number.

SHAFT: stands for sex, hate, alcohol, firearms, and tobacco. Using terms related to SHAFT or anything illegal, including CBD, will cause a message to be heavily filtered by wireless carriers.

Short code: a type of SMS and MMS sending number consisting of a short series of numbers (XXXXX). Short codes are subject to less filtering than other number types and can quickly send to a large number of recipients.

Short Code Registry: a single database of available, reserved, and registered US codes. CTIA, the wireless trade association, oversees and administers the Short Code Registry 

SMCC: stands for short message service centers. A network element in the mobile telephone network. Its purpose is to store, forward, convert, and deliver short message service messages.

SMPP: stands for short message peer-to-peer protocol. SMPP is a protocol that defines the language by which servers that host SMS applications and the operators’ short message service centers (SMSC) speak to enable two-way SMS. 

SMS: stands for short messaging service. This is a type of text message that includes only text or symbols such as emojis.

SMS conversations: Klaviyo's two-way messaging feature. SMS conversations are available when a subscriber texts one of your sending numbers and does not use an SMS keyword. You cannot initiate a conversation; only reply after a customer texts you first. Because branded sender IDs cannot receive inbound messages, this feature is not available for branded sender IDs.

Spam: spam is defined as any electronic commercial message sent without the express consent of the recipient(s).

Spam Act 2003: Australian anti-spam legislation. Designed to protect people from receiving spam, or “unsolicited commercial electronic messages.” It applies to the sending of commercial electronic messages (CEMs) and governs who you can send to and what your messages need to include. 

Subscribe keyword: a type of keyword your customers can use to opt into receiving SMS marketing messages from your brand. One example is JOIN, which is the default in Klaviyo. Subscribe keywords can be customized to fit your brand (see: custom keyword).


TCPA: stands for the Telephone Consumer Protection Act. This act covers the use of automated telephone communications, including phone calls, voicemails, fax machines, and text messages. Under TCPA, sending spam text messages is illegal and can result in fines. Complying with the TCPA involves 2 key parts: consent and opt-in/opt-out choice.

Toll-free number: a type of SMS sending number consisting of 10 digits starting with an eight (1-8XX-XXX-XXXX). Toll-free numbers can be verified, which makes them subject to less filtering than long numbers. You can only have one toll-free number per account.


Unsubscribed from SMS: metric for when a recipient unsubscribes from your SMS messages.

Unwanted messages: unwanted messages (or unwanted messaging) may include unsolicited bulk commercial messages (i.e., spam); “phishing” messages intended to access private or confidential information through deception; other forms of abusive, harmful, malicious, unlawful, or otherwise inappropriate messages; messages that required an opt-in but did not obtain such opt-in or after opt-in was revoked (i.e., the recipient unsubscribed).


Vanity short code: type of short code that allows you to choose what the number is (XXXXX).


WSP: stands for wireless service provider. Commonly used in Canada in place of "carriers."


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