Plain English Meaning

Small pointers you set on the airspeed display to mark the speeds you want to fly at, so you can see them quickly without having to remember the exact numbers.

Full Definition

Movable markers placed around the rim of the airspeed indicator (or set electronically on a digital airspeed tape) that the pilot positions at specific reference speeds so those speeds can be seen at a glance during flight.

Context Anchor

Seen on analog airspeed indicators with movable markers and on glass cockpit displays with settable speed references.

Derivation

The term 'bug' comes from older aviation and engineering use, where a small adjustable marker on a dial was nicknamed a 'bug' because it sat on the face of the like a tiny insect. The name stuck even after the markers became digital.