Plain English Meaning
The signals that come back from an aircraft's transponder and show up on the controller's radar screen, telling the controller who the aircraft is, where it is, and how high it is flying.
Full Definition
The radar display symbols generated when an aircraft's transponder receives an interrogation signal from a ground radar and replies with a coded response containing identification and altitude information. These returns appear on the controller's scope as data blocks showing the aircraft's position, assigned squawk code, and Mode C altitude readout.