Plain English Meaning
Someone on the ground watches your aircraft on a radar screen and tells you which way to fly. You follow their instructions instead of navigating from the cockpit on your own.
Full Definition
A method of navigation in which a ground-based radar facility tracks an aircraft's position and provides vectors, position information, or guidance to the pilot via radio. The controller sees the aircraft as a target on a radar display and issues headings, altitudes, and other instructions to navigate the aircraft along a desired course or to a specific .