The island green on No. 17 at TPC Sawgrass was not the first island green in golf, but by virtue of the very high-profile tournament played there, it is the best-known. It is typical of island greens, too, in that is it a short par-3 hole. Island greens are most commonly found on short par-3 holes, although they are sometimes seen on other types of holes, too.
Geography buffs will know that an island is a piece of land completely surrounded by water. Many island greens in golf are not completely surrounded; most - like the No. 17 at TPC Sawgrass - have a narrow stretch of land connecting the green to its fairway (thereby providing access to the green). Technically, those aren't islands, they're peninsulas.
But "island green" sounds a lot cooler than "peninsular green."
And some island greens really are true islands, completely surrounded by water and not connected to land - sometimes not even by bridge. The 14th hole at the Coeur d'Alene Resort Golf Course in Idaho is a mobile, floating green that can be repositioned, and is reached by water taxi.
Many island greens come with associated drop areas for golfers needing to replay shots that land in the water. The rules vary according to specifics, though, so it's a good idea to inquire in the pro shop about procedures in case you miss the island green.