# Key concepts & glossary

The terms you'll meet throughout AR 51 docs, SDKs, and the API.

## Core system

| Term | Meaning |
|------|---------|
| **OMS** | Operator/Component Management System — the server-communication layer. Components register with it and discover each other. |
| **CVS** | Computer-Vision Server — turns camera images into skeletons and tracked objects. |
| **DGS** | The game/runtime service that engine clients talk to for scene, anchors, and rendering. |
| **MindVision** | The camera brand used in AR 51 systems (referenced in the camera/resolution setup). |
| **Mocap Studio** | The desktop application for recording, calibration, visualization, and export. |

## Tracking data

| Term | Meaning |
|------|---------|
| **Skeleton** | A tracked person's pose — **25 body joints** (plus optional hands) in world space, in **meters**. |
| **Entity** | A registered identity. An entity persists across sessions so the same person keeps a stable `EntityId`. |
| **Entity registration vs detection** | *Registration* defines who to track; *Detection* tracks them. |
| **Tracked object** | A non-person object built from one or more markers (e.g. a basketball, tennis ball). |
| **Marker** | A detected point (e.g. an HSV color blob) used to build tracked objects. |
| **Confidence** | Per-joint reliability score (0–1) included with each skeleton frame. |
| **Capture time** | Unix timestamp (seconds, fractional) stamped on each frame — use it to sync streams. |

## Space & calibration

| Term | Meaning |
|------|---------|
| **Anchor** | A world-space reference point that positions tracked data in your scene. |
| **Guardian** | A play-space boundary (points + height). |
| **Bounding box / active area** | The volume the system tracks within. |
| **Calibration** | Aligning cameras and devices so 3D reconstruction is accurate (camera, device, bounding-box, LED-stage sync). |

## Conventions

- **Units:** meters. **Rotations:** quaternions `(x, y, z, w)`.
- **Coordinate space:** world space for positions; device-local for head/controller rotation.
- **Joint count:** 25 body joints; hands add 21 key points each (→ 67 total points where hands are included).

:::tip
Building on the SDK? Start with the [Data model](/docs/sdk-api/data-model) — it makes every field above concrete.
:::