Many objects are not fundamentally defined by their attriburtes, but rather by a thread of continuity and identity.
Eric Evans, Domain Driven Design
Entities are simple objects that model the things in our domain that have some thread of identity. For the purpose of our workshop, the Purchase Order is the most obvious example of an entity. These objects should be "kept spare" and limited to only attributes and behavior that are essential to the concept. We should be looking to remove behavior and attributes out to other objects.