# Messaging Glossary: A2P, SMS, RCS, CPaaS | ZafeConnect > Plain-language definitions of messaging terms: A2P, P2P, SMS, RCS, CPaaS, SenderID, OTP, HLR lookup, failover, opt-in and more. Canonical URL: https://www.zafeconnect.com/glossary Language: en Last modified: 2026-11-09 ## Messaging glossary URL: https://www.zafeconnect.com/glossary - **10DLC:** In the United States, standard 10-digit phone numbers used for A2P messaging, which carriers require to be registered. - **A2P (application-to-person):** Messages sent automatically by software to a person, such as codes, alerts and reminders. - **AIT / SMS pumping:** Artificially inflated traffic: attackers trigger large numbers of verification messages to numbers they profit from. Rate limits, number validation and monitoring reduce the risk. - **Alphanumeric sender ID:** A sender name of letters and digits, up to 11 characters, shown instead of a phone number. Allowed and regulated differently by country, and usually cannot receive replies. - **API:** Application programming interface: the way your software sends messages and reads results from a messaging platform. - **Carrier billing (MOP):** A payment method where a purchase is charged to the customer’s mobile phone bill or prepaid balance. - **Chatbot:** Software that answers customer questions automatically in a messaging channel and can hand over to a person. - **CPaaS:** Communications Platform as a Service: a cloud platform that gives applications messaging and voice through APIs. - **Delivery receipt (DLR):** A status report from the network about whether a message was delivered. Detail and availability vary by country and operator. - **Direct connection:** A connection between a messaging provider and a mobile operator with no other provider in between: the shortest route a message can take. - **Failover:** Automatically switching to an alternative route or region when a network has problems, so messages are still delivered. - **GDPR:** The EU General Data Protection Regulation, which governs how personal data, including phone numbers, may be processed. - **HLR lookup:** A query that checks whether a phone number is active and, where available, which network it belongs to. - **Intelligent routing:** Choosing the best available route for each message, and moving traffic to another route if the first one has problems. - **IVR:** Interactive voice response: automated phone menus that react to keypad or spoken input. - **Knowledge base:** A central collection of answers that powers chatbots, agents and self-service. - **LOA (Letter of Authorization):** A signed document in which the owner of a sender name authorises another party, such as ZafeConnect, to register and manage it on its behalf. Required for SenderID Protection. - **Long code (virtual number):** A normal-length phone number used to send and receive messages or calls. - **MMS:** Multimedia Messaging Service: messages with images, audio, video or contact cards. - **MO / MT:** Mobile originated: a message sent from a handset to a service. Mobile terminated: a message delivered to a handset. - **Number masking:** Connecting two parties through a temporary intermediate number so neither sees the other’s real number. - **Omnichannel:** Reaching customers across several channels, such as SMS, RCS, email and chat apps, with one integration and shared reporting. - **Opt-in:** A customer’s clear agreement to receive messages from you. Marketing messages generally require it. - **Opt-out:** The customer’s ability to stop receiving messages, for example by replying STOP. It should be easy and honoured promptly. - **OTP (one-time passcode):** A single-use code sent to a user to verify identity or a phone number. - **P2P (person-to-person):** Messages sent from one person to another, such as texting a friend. - **Partner direct:** A direct operator connection that a partner runs and that a provider uses to extend its reach to more countries. - **Push notification:** A short message that an app sends to a user’s device, shown on the lock screen or in the notification area. - **RCS:** Rich Communication Services: a modern messaging standard with branded, interactive messages in the phone’s default messaging app. - **SenderID:** The name or number shown as the sender of a message. - **SenderID Protection:** A service that registers your sender name so others are kept from using it, where operators or registries support protection. At ZafeConnect it requires an LOA and has a separate monthly fee. - **SenderID registration:** Getting a sender name approved for use in a country. Some countries require it before you can send with the name. - **Short code:** A short phone number, often 5–6 digits, used for high-volume messaging in some countries. - **SMPP:** Short Message Peer-to-Peer: a protocol that messaging systems use to exchange SMS with providers and operators. - **SMS:** Short Message Service: text messages. A segment holds up to 160 characters in the standard GSM alphabet, or 70 with Unicode characters; longer messages are split into segments. - **SMS aggregator:** A messaging provider that connects many businesses to many mobile operators through one integration. The route mix behind it, not the label, decides delivery quality. - **SMS API:** A way for software to send text messages and read their delivery status through HTTP requests. ZafeConnect offers a REST API with signed delivery webhooks. - **SMS gateway:** The connection or software through which a business sends messages into a provider’s network and on to the mobile operators. Often offered as an API. - **SMS segment:** One unit of an SMS. Longer texts are split into several segments, which can affect cost. - **SMS spoofing:** Sending messages that appear to come from a trusted sender name, often as part of phishing (smishing). - **Template message:** A pre-approved message format, required by some channels such as WhatsApp for business-initiated messages. - **Throughput:** How many messages per second a route or platform can send. - **Toll-free number:** A phone number that is free for the caller, also usable for messaging in some countries. - **Transactional message:** A message that confirms or informs about something the customer did or needs to know, such as a passcode, a receipt or a delivery update. - **Two-way messaging:** Messaging in which customers can reply, so notifications become conversations. - **Upstream provider:** A company that supplies a messaging provider with connections to mobile operators. Using several avoids depending on one. - **Voice API:** An interface that lets software place phone calls, play messages and build voice flows.