1. <programming, operating system> A simple item of data that identifies a resource. For example, a Unix file handle identifies an open file and associated data such as whether it was opened for read or write and the current read/write position. On the Macintosh, a handle is a pointer to a pointer to some dynamically-allocated memory. The extra level of indirection allows on-the-fly memory compaction or garbage collection without invalidating application program references to the allocated memory.
2. <jargon> An alias used intended to conceal a user's true identity in an electronic message. The term is common on Citizen's Band and other amateur radio but, in that context usually means the user's real name as FCC rules forbid concealing one's identity.
3. <networking> domain handle.