Plain English Meaning
An instrument on the panel that shows whether the nose is pointing up or down and whether the wings are level or banked, by comparing them to a steady artificial horizon.
Full Definition
A gyroscopic flight instrument that displays the airplane's pitch and bank relative to the natural horizon. It uses a spinning gyro to hold a stable reference, against which a miniature airplane symbol moves to show the aircraft's orientation in real time.
Context Anchor
Seen in analog instrument flying when using the attitude indicator as the main reference for airplane .