> ## Documentation Index > Fetch the complete documentation index at: https://docs.surge.app/llms.txt > Use this file to discover all available pages before exploring further. # Glossary > Definitions for Surge and A2P messaging terms: Account, Brand, Campaign, CSP, TypeID, Dashboard User, User, and more. Terms used in Surge documentation, the API, and the broader A2P messaging industry. *** **A2P messaging** Application-to-person messaging. Text messages sent programmatically from software to a person's mobile phone, as opposed to P2P (person-to-person) messages between individuals. Surge is an A2P platform. *** **Account** A resource in Surge that represents one messaging brand. An account owns phone numbers, campaigns, contacts, conversations, and messages. In carrier terminology, an account corresponds to a *brand*. See also: *Project*, *User* *** **Audience** A named, reusable list of contacts. Audiences are used to send repeated messages to the same group — weekly newsletters, customer cohorts, geographic segments. Created via `POST /accounts/{account_id}/audiences` and populated by adding contacts. Blast an audience by passing its ID in the `to` array when creating a blast. See also: *Blast*, *Contact* *** **Blast** A one-time send to a list of recipients. A blast is created with a `from` number, a `body`, and a `to` array of phone numbers, contact IDs, or audience IDs. Unlike regular messages, blasts are not threaded into conversations. Use a blast for ad-hoc sends; use an audience when the same list receives messages repeatedly. See also: *Audience* *** **Brand** The carrier industry term for the legal business entity behind a messaging campaign. In Surge, an *Account* is your brand. *** **Campaign** A registered use case for sending messages. Campaigns describe what you're sending, to whom, and how recipients opted in. Every phone number that sends production traffic must be attached to an approved campaign. *** **Campaign Service Provider (CSP)** An intermediary registered with The Campaign Registry that submits brand and campaign registrations on behalf of its customers. Surge is a CSP. Most Surge customers don't need to become CSPs themselves, but we can support you in that endeavor if you wish — see [The Campaign Registry and Becoming a CSP](../concepts/tcr). *** **Contact** A phone number record within an account. When you message someone or they message you, Surge creates a contact to represent that number. Contacts track opt-out state and can carry metadata. *** **Conversation** A thread of messages between your phone number and a specific contact. All inbound and outbound messages with the same contact on the same number belong to one conversation. *** **CSP** See *Campaign Service Provider*. *** **Dashboard User** A person who logs in to `hq.surge.app` to manage Surge: API keys, billing, webhooks, phone numbers, and account configuration. Distinct from an API-provisioned User. A Dashboard User can belong to multiple projects. *** **E.164** The international phone number format used throughout the Surge API. E.164 numbers start with `+` followed by the country code and subscriber number, with no spaces or punctuation. Example: `+18015551234`. *** **GSM-7** The character encoding used for standard SMS. Covers the basic Latin alphabet, digits, and common punctuation. Messages using only GSM-7 characters fit 160 characters per segment (153 in multi-part). See [SMS Segments & Encoding](../concepts/sms-segments). *** **10DLC** Ten-digit long code. This can be used to signify what Surge calls "local" numbers, that is non-toll free VoIP numbers used for sending messages. This also refers to the US carrier framework for A2P messaging using standard 10-digit phone numbers. Requires brand and campaign registration via The Campaign Registry. *** **Opt-in** Explicit permission from a recipient to receive text messages. Carriers require documented opt-in consent before you send any text messages. *** **Opt-out** A recipient's request to stop receiving messages, typically by replying STOP. Once opted out, sending to a contact returns an `opted_out` error. *** **MMS** Multimedia Messaging Service. An extension of SMS that supports sending images, GIFs, PDFs, and other media in addition to text. MMS segments can carry more data than SMS segments, but delivery depends on the recipient's carrier and handset supporting MMS. See also: *SMS*, *Segment* *** **Project** The top-level Surge tenant. Your company or product is a project. A project contains one or more accounts, holds your API keys and billing, and configures webhooks. You get one project when you sign up for Surge. *** **Segment** The carrier's billing unit for SMS. One segment is 140 bytes. A GSM-7 message fits 160 characters in one segment; a message using UCS-2 (e.g., with emoji) fits only 70 characters. See [SMS Segments & Encoding](../concepts/sms-segments). *** **Short code** A 5- or 6-digit phone number (e.g., `12345`) used for high-volume A2P messaging. Short codes support very high throughput and are often used for large-scale marketing programs. Purchasing a short code requires a support request — they are not available via the API. Subject to their own carrier registration process separate from 10DLC. *** **SMS** Short Message Service. The standard protocol for sending text-only messages up to 160 GSM-7 characters (or 70 UCS-2 characters) per segment. The default protocol for Surge messages. When a message has attachments or exceeds 10 segments, Surge automatically upgrades to MMS. *** **TCR** See *The Campaign Registry*. *** **Toll-free number** A phone number with an 8xx area code where the call or message cost is borne by the called party, not the caller. Surge purchases new toll-free numbers in `833`, `844`, `855`, `866`, `877`, and `888`; the original `800` prefix is mostly exhausted and is available only via port-in. Toll-free numbers go through a separate verification process from 10DLC local numbers. Available via the API (`type: "toll_free"`); verification currently requires the dashboard. *** **The Campaign Registry (TCR)** The industry body that registers A2P 10DLC brands and campaigns. US mobile carriers use TCR to verify who is behind phone numbers sending text messages. Surge submits registrations to TCR as your CSP. *** **TypeID** The format used for all Surge resource IDs. A TypeID is a type prefix followed by a 26-character alphanumeric ID. Examples: `acct_01jrzhe8d9enptypyx360pcmxj` (account), `msg_01jrzhe8d9enptypyx360pcmxk` (message), `cpn_01jrzhe8d9enptypyx360pcmxl` (campaign). *** **UCS-2** The character encoding used when a message contains characters outside the GSM-7 set (emoji, accented characters, curly quotes, etc.). UCS-2 messages fit only 70 characters per segment. See [SMS Segments & Encoding](../concepts/sms-segments). *** **User** A person provisioned via the Surge API (via `POST /accounts/{account_id}/users`) who interacts with embedded UI components. Users do not log in to the Surge dashboard; they authenticate to embedded components with a short-lived token. Distinct from: *Dashboard User*. *** **Webhook** An HTTP callback Surge sends to your server when something happens: a message arrives, a campaign is approved, a contact opts out. You configure a webhook endpoint URL in the dashboard, and Surge POSTs events to it in real time.