This article is from the Golf FAQ, by marcelo@nntpserver.Princeton.EDU (Marcelo A. Gallardo) with numerous contributions by others.
Hitting a fairway is exactly that, your ball comes to rest off the tee
(except par 3's) in the fairway cut of grass.
Hitting a green in regulation means that your ball will be on the
putting surface in 1 shot on a par 3, 2 shots (or less) on a par 4 and
3 shots (or less) on a par 5.Just subtracting 2 putts from the par
gives you the "Regulation" number of strokes to reach the green.