Plain English Meaning
The radar controller who looks after you in the first few minutes after takeoff, telling you which way to turn and how high to climb until you are passed on to the next controller.
Full Definition
An air traffic control facility, normally co-located with an approach control, that uses radar to provide separation, vectors, and climb instructions to IFR aircraft (and participating VFR aircraft) immediately after takeoff until they are handed off to an en route center or other facility.
Context Anchor
Seen on departure procedure notes, setups, and radar- where is told which controller or frequency to after takeoff.