[pRED*]

This has actually changed since that blog post was written.

An entity is only understood by the game code, an edict is the engines representation of an entity (and used to network data about the entity to players).

All edicts should have a matching entity, but some entities can exist without an edict. Logic style entities that don't have a client side entity won't have an edict, as they never get networked and exist purely for server side logic purposes.