Normally, definitions are contained in 14 CFR 1. That part does not define takeoff nor does it define landing. Since they are not defined there, and to my knowledge anywhere in the regulations, a generalized definition of takeoff or landing.
Therefore, the common definition (or really usage) of takeoff or landing would apply, at least in legal matters.
One should be careful deriving definitions from advisory material.
It is noteworthy that for different aircraft, takeoff may mean different things. For example, on a 787, when the mains leave the surface of the runway, we might consider that takeoff. However, a R22 helicopter, hovering on a ramp, or taxiing to a runway may not be considered as having taken off, even though it is not in contact with the surface or a surface structure.
Takeoff has different nuances, and mechanics, for different aircraft, and even different operations. There is no one regulatory definition, although some aspects of a definition may be inferred from some regulations. Advisory material do not constitute regulations.