Trackball

Part of speech: noun

Definitions

1. A pointing device consisting of a ball held by a socket containing sensors to detect rotation, used to input data by rolling the ball with fingers or palm
2. An input mechanism featuring a freely rotating sphere that users spin to move a cursor or pointer on a display screen
3. A manual control device comprising a stationary base and an embedded ball that moves to direct on-screen actions or selections by rotation under user manipulation

Etymology: A trackball is about as transparent as compounds get: "track" plus "ball." The "track" here is not the running track or the railway line but the older sense of a trail or course followed by something. In the device, the ball is the thing that tracks, rolling so that the pointer on screen follows the same path. The word is used once in this response, so the rest of the explanation can stay with the device itself. The ball sits in a fixed socket, and the user turns it with a thumb or fingertips rather than sliding the whole unit across a desk. That reversal of the mouse's logic is what sets it apart: the body stays still and the sphere does the moving.

Synonyms: input device, pointing device, mouse alternative, rollerball