Airspeed refers to the speed of an aircraft relative to the surrounding air. It is a crucial measurement for pilots, as it affects lift, drag, and overall flight performance. Airspeed is typically measured in knots or miles per hour and can be indicated on the aircraft's instruments. There are different types of airspeed, including true airspeed, indicated airspeed, and ground speed. True airspeed is the actual speed of the aircraft through the air, while indicated airspeed is what the pilot reads on the airspeed indicator. Ground speed measures how fast the aircraft is moving over the ground, which can be affected by wind conditions.