DTOs are not Objects

A DTO is a representation of such a piece of data mapped into an object-oriented language. That still doesn’t make them objects in the sense of encapsulation. It would be impossible. Since all input is suspect, we can hardly enforce any invariants at all.

 http://blog.ploeh.dk/2011/05/31/AtTheBoundariesApplicationsAreNotObjectOriented.aspx

You usually can’t send the domain object itself, because it’s tied in a web of fine-grained local inter-object references. So you take all the data that the client needs and bundle it in a particular object for the transfer—hence the term.

Fowler http://www.drdobbs.com/errant-architectures/184414966