A device that connects a PDA to something less portable -- typically a desktop or laptop computer, but sometimes a server with lots of cradles attached over the network.
The name comes from the fact that the PDA typically stands upright in it, cradled by a cupped surface while it synchronizes its data with the other computer.
Cradles generally use either serial (DB-9) or USB connections; in the latter case, the cradle may also serve as a battery charger. Cradles take other physical forms; some keyboards for PDAs are also cradles, and laptop users generally want something compact and foldable like a simple cable that plugs into the bottom of the PDA.