> and pilots must be very sure they have clearance before entering a runway
The word "clearance" is used uniquely in the context of landing and departing exactly to avoid mistakes and has to be repeated again by the aircraft before ATC confirms.
The terms "cleared to land" and "cleared for takeoff" are extremely specific (a regulation written in blood like many aviation rules), but "cross runway" and "line up and wait" also give permission for aircraft to enter the runway.
The word "cleared" is often used for IFR clearance delivery as well which gives you permission to navigate via a planned route to a particular point, so it's much more common than just takeoffs and landings.
True in terms of phraseology (i.e. the actual word is not used in voice ATC communications), but all ATC instructions are generally referred to as clearances.
The word "clearance" is used uniquely in the context of landing and departing exactly to avoid mistakes and has to be repeated again by the aircraft before ATC confirms.