# ML-Agents Toolkit Glossary

- **Academy** - Singleton object which controls timing, reset, and
  training/inference settings of the environment.
- **Action** - The carrying-out of a decision on the part of an agent within the
  environment.
- **Agent** - Unity Component which produces observations and takes actions in
  the environment. Agents actions are determined by decisions produced by a
  Policy.
- **Decision** - The specification produced by a Policy for an action to be
  carried out given an observation.
- **Editor** - The Unity Editor, which may include any pane (e.g. Hierarchy,
  Scene, Inspector).
- **Environment** - The Unity scene which contains Agents.
- **Experience** - Corresponds to a tuple of [Agent observations, actions,
  rewards] of a single Agent obtained after a Step.
- **External Coordinator** - ML-Agents class responsible for communication with
  outside processes (in this case, the Python API).
- **FixedUpdate** - Unity method called each time the game engine is stepped.
  ML-Agents logic should be placed here.
- **Frame** - An instance of rendering the main camera for the display.
  Corresponds to each `Update` call of the game engine.
- **Observation** - Partial information describing the state of the environment
  available to a given agent. (e.g. Vector, Visual)
- **Policy** - The decision making mechanism for producing decisions from
  observations, typically a neural network model.
- **Reward** - Signal provided at every step used to indicate desirability of an
  agent’s action within the current state of the environment.
- **State** - The underlying properties of the environment (including all agents
  within it) at a given time.
- **Step** - Corresponds to an atomic change of the engine that happens between
  Agent decisions.
- **Trainer** - Python class which is responsible for training a given group of
  Agents.
- **Update** - Unity function called each time a frame is rendered. ML-Agents
  logic should not be placed here.