I was going through old mail and found something that Dennis had sent me some time ago. He says:
I'm sure this one is old hat to you .NET code slingers, but it caught my attention. In a course on ADO.NET, the instructor was explaining that ADO.NET uses XML for moving data around. His PowerPoint slide said, "ADO.NET takes care of transporting SML data and rehydrating it back as a DataSet."[Mike here] This is indeed programmer jargon. I'd bet a nickel that our editors would probably quash the term. It has made it into articles and whitepapers, but I don't find any instances of it in our formal documentation, with the notable exception of the docs for BizTalk Server. (Example.)
This article has a good explanation of how "rehydrate" is used in programmer context. The basic notion is that a program entity (an object) has to be moved (to another computer, for example). Its running bits cannot be transported as is, so the object is "serialized" into a text-like representation of its definition and state. The representation is transported and then, of course, it is deserialized, aka "rehydrated" on the target machine. I personally like the imagery, FWIW.