POCO - Defined

EF Code First enables you to use “POCO” – Plain Old CLR Objects – to represent entities within a database. This means that you do not need to derive model classes from a base class, nor implement any interfaces or data persistence attributes on them. This enables the model classes to be kept clean, easily testable, and “persistence ignorant”.

http://weblogs.asp.net/scottgu/archive/2010/12/08/announcing-entity-framework-code-first-ctp5-release.aspx