Archetype (ECS)
In an entity component system, the unique set of component types an entity carries — all entities with exactly the same set are stored together in dense, parallel arrays.
Add or remove a component and the entity moves to a different archetype. The payoff is that a system wanting everyone with Position and Velocity finds them as one contiguous block of memory and iterates straight through without jumps — friendly to the CPU cache and easy to vectorise.
This "archetypal" storage (Unity DOTS, Flecs) stands against the "sparse set" model (EnTT), which indexes each component type separately instead. Archetypes iterate faster but pay whenever entities frequently change their component set, since each change means a move.