Extracted from here
Entity This is the base class of Mass that holds pointers to all of its Fragments
Fragment Holds the data/state for an Entity in tightly packed arrays (e.g. transform, velocity, current LOD, etc.)
Archetype Entities with identical Fragment composition that are grouped together. Entity composition can change at runtime resulting in Archetype migration
Trait Group fragments together and typically represent Entity features (e.g. Movement, ZoneGraph Navigation, SmartObject User)
Tags Archetype-level, Dataless Fragments that can be used by Queries for filtering archetypes based on their presence or absence
Chunk Fragment Fragments that are applied to a subset of Entities in an Archetype instead of directly to a single Entity
Shared Fragment Fragments with data that are shared with multiple entities for memory optimization purposes
Processor Where logic execution occurs in Mass. Processors can change values of a Fragment as well as composition of Entities (adding or removing).
Entity Query A query used by processors that filters archetypes based on fragment and/or tag requirements. The EntityQuery returns batches of fragments without regard to the individual Entity identifiers
Mass Spawner System for adding Entities to a level at runtime
Mass Entity Config Asset that defines the Mass agent to spawn by specifying traits of the Entity