Entities vs. Value Objects

A value object can become an entity depending on the situation. ... If the requirement of the search functionality of your application says that, the search criteria should be saved in the database and the user can do the same search from the list of saved search criteria’s. In this scenario SearchCriteria has its own identity and thus it is an entity instead of being a value object. ... 
remember that Aggregate Roots may comprise one or many Entities and Value Objects

http://www.codeproject.com/Articles/339725/Domain-Driven-Design-Clear-Your-Concepts-Before-Yo

Value objects are immutable. see fig 2 example in http://msdn.microsoft.com/en-us/magazine/dd419654.aspx