# Glossary URL: https://www.atmee.ai/docs/v2/getting-started/glossary > The words these docs use, each in a sentence or two, with a link to where it is explained in full. Every term has its own link: `/docs/v2/getting-started/glossary#avatar`, `/docs/v2/getting-started/glossary#credit` and so on. ## API key A secret your server sends with every API call, in the `X-Api-Key` header. It belongs to your Atmee account: what it may do is set by its [scopes](#scope), what it may spend by its [spend cap](#spend-cap). It must never reach a browser: a key in page JavaScript can be read by every visitor. Create one in **Studio → API**. See [API keys](/docs/v2/api/api-keys). ## Avatar A talking video character, built on one [model](#model). It is made from a [portrait](#portrait), a [voice sample](#voice-sample) and a [persona](#persona), and can answer from [knowledge](#knowledge) files. Each avatar belongs to one account and has an [avatar ID](#avatar-id). Make one in [Studio](#studio) or with [Create an avatar](/docs/v2/api/create-avatar). ## Avatar ID The identifier of one [avatar](#avatar), passed as `avatarId` when you start a [session](#session). In Studio it's the UUID in the avatar's editor address, `/studio/avatars//edit`, and the API returns it from `POST /v1/avatars`. ## Avatar mode The mode where you bring your own voice agent, with its own speech recognition, language model and voice, and Atmee renders only the [avatar](#avatar)'s face, in sync with your agent's audio. Start it with the [LiveKit Agents plugin](#livekit-agents-plugin) or `POST /v1/avatar_sessions`. It costs half of [Behavior-driven Full-stack](#behavior-driven-full-stack). ## Avatar session A [session](#session) in [Avatar mode](#avatar-mode): the avatar joins your LiveKit [room](#room), or one Atmee hosts, and speaks your agent's audio. See the [LiveKit Agents plugin](/docs/v2/livekit-plugin/livekit-agents-plugin). ## Behavior-driven Full-stack The mode where Atmee runs the whole conversation: behavior (powered by [Causeur](#causeur)), the language model, speech recognition, the voice and the face. Your side is one server endpoint that calls `POST /v1/sessions` and a page that joins the [room](#room). See the [Quickstart](/docs/v2/api/quickstart). ## Behavior-Driven Voice Mode The mode where Atmee runs the conversation with [Causeur](#causeur) and the avatar's voice, with no video. Your server calls `POST /v1/speech_sessions` and your client streams audio over a WebSocket. ## Causeur Atmee's behavior model. It decides how an avatar acts, not just what it says: personality, emotion, timing and active listening. It runs in [Behavior-driven Full-stack](#behavior-driven-full-stack) and [Behavior-Driven Voice Mode](#behavior-driven-voice-mode). ## Credit The unit everything is paid in. On an Atmee V1 [model](#model), a [Session API](#session-api) session costs 1 credit per minute and an [avatar session](#avatar-session) 0.5; Atmee V2 costs twice that. Your [plan](#plan) includes credits each month, and you can buy more under **Studio → Billing**. See [Costs](/docs/v2/api/overview#costs). ## Knowledge Documents an [avatar](#avatar) answers from: PDFs, Word files, text, Markdown, HTML or CSV, up to 20 files. Add them when you create the avatar, or replace them later. ## LiveKit The real-time video and audio service a conversation runs over. With the [Session API](#session-api) Atmee runs it for you; with the [LiveKit Agents plugin](#livekit-agents-plugin) you use your own LiveKit project. ## LiveKit Agents plugin A Python package for developers who already run a voice agent on LiveKit Agents. Your agent decides what to say; the plugin adds an Atmee [avatar](#avatar) that says it. See the [LiveKit Agents plugin](/docs/v2/livekit-plugin/livekit-agents-plugin). ## Model The AI that renders an [avatar](#avatar)'s face: **Atmee V2**, our latest and most human-like, or **Atmee V1**, realistic at half the [credits](#credit). An avatar's model is set when it is created (`engine` in the API). See [Models](/docs/v2/getting-started/models). ## Persona Who an [avatar](#avatar) is: its name, personality, greeting, how it introduces itself, and the rules it must not break (guardrails). The persona and the [knowledge](#knowledge) decide what the avatar says. ## Plan Your Atmee subscription: Free, Starter, Growth, Pro, Scale or Enterprise. It sets the [credits](#credit) you get each month, the longest session and how many sessions run at once. API access starts on Starter, and Atmee V2 on Growth. See the [pricing page](https://www.atmee.ai/pricing). ## Portrait The image an [avatar](#avatar)'s face is rendered from: one photo or picture showing the whole head with some margin around it. ## Room The live video call a [session](#session) takes place in. The avatar and your user each join it as a participant. Your page joins with the [server URL and user token](#user-token) the session returns. ## Scope A permission on an [API key](#api-key). `sessions` lets it start sessions, `avatars:read` and `avatars:write` let it read and manage avatars. Give each key only the scopes it needs. See [Scopes](/docs/v2/api/api-keys#scopes). ## Session One live conversation between one user and one [avatar](#avatar). Your server starts it with `POST /v1/sessions`; it ends when the user leaves or its time runs out, and it is billed by the minute in [credits](#credit). One avatar holds one session at a time. ## Session API `POST /v1/sessions`, the endpoint that starts a [Behavior-driven Full-stack](#behavior-driven-full-stack) session. ## Spend cap A limit on how many [credits](#credit) one [API key](#api-key) may spend, in total, per month or per day. When it is reached, new sessions with that key are refused. See [Caps](/docs/v2/api/api-keys#caps). ## Studio Atmee's web app at [atmee.ai/studio](/studio), where you create and manage avatars, API keys and billing. Everything you do with the API, you can also see there. ## User token What your page needs to join a [session](#session)'s [room](#room). `POST /v1/sessions` returns a `serverUrl` and a `userToken`, a short-lived token good for that one room only. Your server passes both to the page and keeps the [API key](#api-key) to itself. ## Voice sample A recording of the voice an [avatar](#avatar) should speak with: 10 to 60 seconds of clear speech from one person. **Building with an AI agent?** The agent skills, the MCP server and the `atmee` CLI are explained on their own pages. - [Build with AI agents](/docs/v2/agents): What the skills, the MCP server and the CLI are, and how they fit together.