Plain English Meaning

A box on the aircraft that knows where it is, which way it's pointing, and how fast it's moving — purely by sensing its own movement from a starting point. It needs no outside signal to work.

Full Definition

A self-contained navigation device that uses ring laser gyroscopes and accelerometers to continuously sense the aircraft's motion and rotation in three dimensions. From an initial known position, it calculates and outputs aircraft position, attitude, heading, ground speed, and acceleration without relying on any external signal such as GPS, radio, or ground-based navaid.

Context Anchor

Seen in modern aircraft navigation, flight , and discussions, especially when checking that feed attitude, heading, and navigation information to the .