Identity, entity and continuity - c/o Evans (2009)

"Many things are defined by their identity, and not by any attribute. In our typical conception, a person ... has an identity that stretches from birth to death and even beyond. That person's physical attributes transform and ultimately disappear. The name may change. Financial relationships come and go. There is not a single attribute of a person that cannot change; yet the identity persists. Am I the same person I was at age five? This kind of metaphysical question is important in the search for effective domain models. Slightly rephrased: Does the user of the application care if I am the same person I was at age five? 

A conceptual identity has to be matched between multiple implementations of the objects, its stored forms, and real-world actors such as a phone caller. Attributes may not match." p.90.

"Object modeling tends to lead us to focus on the attributes of an object, but the fundamental concept of an ENTITY is an abstract continuity threading through a life cycle and even passing through multiple forms.

"Some objects are not defined primarily by their attributes. They represent a thread of identity that runs through time and often across distinct representations. Sometimes such an object must be matched with another object even though the attributes differ. An object must be distinguished from other objects even though they might have the same attributes. Mistaken identity can lead to data corruption.

An object defined primarily by its identity is called an ENTITY. ...

Domain-Driven Design

Of course, most "ENTITIES" in a software system are not people or entities in the usual sense of the word. An ENTITY is anything that has continuity through a life cycle and distinctions independent of attributes that are important to the application's user. It could be a person, a city, a car, a lottery ticket, or a bank transaction." p.91.

Eric Evans, (2009). Domain-Driven Design: Tackling Complexity in the Heart of Software, Model-Driven Design. Addison-Wesley.
[Emboldened text as per book.]