transient keyword suggests that the object should not be serialized, nor persisted. You can use it if you don't want to serialize heavy objects (such as Wrappers, for example, which can contain a lot of business logic).
@Transient annotation suggests that the object should not be persisted (if you've been playing with Hibernate, for example), but it can be serialized.
I've included the annotation explanation, because I remember being confused by the two. :-)
