From The Collaborative International Dictionary of English v.0.48 :
Putting green \Putt"ing green\ (Golf)
The green, or plot of smooth turf, surrounding a hole. "The
term putting green shall mean the ground within twenty yards
of the hole, excepting hazards." --Golf Rules.
[Webster 1913 Suppl.]
From WordNet (r) 3.0 (2006) :
putting green
n 1: an area of closely cropped grass surrounding the hole on a
golf course; "the ball rolled across the green and into the
bunker" [syn: green, putting green, putting surface]