Plain English Meaning
A small marker on the controller's radar screen that shows where their cursor is pointing, moved by rolling a trackball with their hand.
Full Definition
A marker on an air traffic control radar display showing the current position of the controller's trackball-controlled cursor. The controller moves the trackball to point this symbol at a specific location on the screen, typically to attach data, measure distances, or designate a target.
Context Anchor
Seen in explanations or figures of ARTS III/DBRITE air traffic control radar displays, not as a cockpit instrument indication.
Derivation
A trackball is an input device — like an upside-down mouse — where the user rotates a with their fingers or palm to move a cursor. The is simply the on-screen marker that follows the trackball's movement.