Primitives

Foundational ECS concepts that show up everywhere in Bevy. The types on these pages are the vocabulary other crates speak — once you know them, you can read any Bevy code.

All of these live in bevy_ecs. The pages here are concept-oriented; see the crate page for the implementation tour.

Pages

Concept	What it is
Entity	The opaque ID for an in-world thing.
Component	A piece of data attached to an entity.
Bundle	A typed group of components inserted as a unit.
Resource	A globally-unique singleton on the world.
World	The container. Owns entities, components, resources, and schedules.
System	A function that reads and writes the world. Parameters declare access.
Schedule	A directed graph of systems with ordering, run conditions, and parallel execution.
Observer	A reactive function fired in response to ECS lifecycle events.
Query	A typed iteration over entities matching a component signature.

See also

• bevy_ecs for the implementation map.
• Architecture for how these compose into the App.
• Glossary for short definitions of all the terms.