Plain English Meaning
It is the airspeed shown on the cockpit gauge after small built-in errors from how the airspeed system is installed and how the instrument itself reads have been corrected. It gives a more accurate picture of the airplane's speed through the air than the raw indicated reading.
Full Definition
Calibrated airspeed is the indicated airspeed of an aircraft, corrected for installation error and instrument error. At sea level in standard atmospheric conditions, calibrated airspeed equals true airspeed.