What is difference between ground speed and airspeed? Is ground speed used only for takeoff or is it used for flight too?
The ground speed is the speed the aircraft is making over ground below.
The indicated airspeed (IAS) is the speed shown on the airspeed indicator. This will be different than the ground speed for various reasons, such as wind and the attitude of the aircraft. For example, if the aircraft is diving then the IAS will be greater than the ground speed. In fact, if the aircraft were diving straight down, then the ground speed could be 0 while the IAS was hundreds of knots per hour.
The indicated airspeed is the usual measure used in flight.
The ground speed can be calculated to estimate the time of arrival of the aircraft at some destination.