Plain English Meaning
KTAS is how fast the airplane is really moving through the air, measured in knots. The cockpit airspeed indicator reads a lower number at altitude because the air is thin; KTAS is that reading corrected to show the actual speed.
Full Definition
KTAS is the aircraft's true airspeed expressed in knots — the actual speed of the aircraft through the surrounding air mass, corrected for the effects of altitude and temperature on indicated airspeed. One knot equals one nautical mile per hour.
Context Anchor
Seen in performance charts, flight planning, and discussions where true airspeed is compared with or indicated cockpit .