Originally Posted by
Saint Jack
'Aircraft hours' (referring to entries in the aircraft log books) are the total hours from brakes-off on the runway for the take-off run to a full-stop (or almost full-stop) after landing while still on the runway. Run-up time and taxi time is not included. This is more often referred to as 'time in service' and is primarily used to schedule the required aircraft maintenance actions
FARs define Aircraft Hours as
"The airborne hours of aircraft computed from the moment an aircraft leaves the ground until it touches the ground at the end of a flight", so not quite the same.