Entities

An entity is a singular thing.

What Actually is an Entity?

An entity is basically just a unique ID that allows a thing to be identified, the entity itself does not store any components (data), instead it is just an index that the components can be grouped with. The entity includes a couple of helper functions to allow components to be managed (adding and removing), and to allow the entity to be destroyed - but keep in mind these are only helpers, the component data is not actually stored in the entity, it is stored elsewhere in the engine (see the ComponentManager and EntityManager for details about this).

Where are Entities Stored?

See the EntityManager for details.

Granularity

The granularity of this will depend on the design and choices for a game - a player could be a single entity, or it could be multiple entities, with one for the player's head, another for the player's torso etc. This is simply a design choice, and working out the best approach is left to the game developer.