Plain English Meaning
Aircraft on the radar screen that the computer has paused tracking on. The blip and label are still shown, but the system is waiting for the controller to sort something out before it resumes following the aircraft automatically.
Full Definition
Aircraft data blocks on an ARTS III or DBRITE radar display that have been temporarily held in a non-tracking state by the controller, usually because the aircraft is in a coast situation, has lost transponder return, or is being held aside while the controller resolves identification or handoff issues. The target symbol and tag remain visible but are not actively updated by the automation system until the controller re-establishes tracking.