It's turned in to plain text that can be re-created in to the objects. From Wikipedia [1]:

"[...] serialization is the process of translating data structures or object state into a format that can be stored (for example, in a file or memory buffer, or transmitted across a network connection link) and "resurrected" later in the same or another computer environment"

[1] http://en.wikipedia.org/wiki/Serialization