A Discussion on Domain Driven Design: Entities

My last post was intended to help better explain how the ubiquitous language forms the back bone of Domain Driven Design (DDD). I am hoping that this post helps to explain some of the more foundational artifacts of DDD, namely Entities. What is an entity? Is it a business object? Is it a class that has persistence? Is it a sentient being manifested in the form of a polymorphic construct that is based on a real world object? Ok well maybe the latter is definitely out of scope but as we see there are many possibilities of what an entity is. Hopefully I will help to shed some light on the subject. Either that or I will help to perpetuate the existing confusion. At least we go somewhere!