Plain English Meaning
An airspeed gauge that shows your real speed through the air, not just what the simple airspeed dial reads. You set the altitude and temperature on a small dial, and it does the math for you.
Full Definition
A cockpit airspeed instrument that displays true airspeed directly, automatically correcting indicated airspeed for pressure altitude and outside air temperature. The pilot sets the current pressure altitude opposite the outside air temperature on a small subscale, and the instrument's inner scale then reads true airspeed without the need for a separate flight computer calculation.
Context Anchor
Seen when studying types of airspeed and when comparing cockpit airspeed indications with speeds.