Definition: Foursomes is a competition format in which a team is comprised of two players, and those two golfers alternate hitting the same ball (which is why Foursomes is also very commonly called "alternate shot").
The first player tees off, the second player hits the second shot, the first player hits the third shot, and so on until the ball is holed. Players alternate hitting tee shots so that the same player doesn't hit every drive.
Foursomes can be played as stroke play or match play. As match play, Foursomes is one of the formats used in the Ryder Cup, the Presidents Cup, the Solheim Cup, and other top professional and amateur team events.
Here's a hint for Foursomes strategy: Try to determine before the round which are the toughest driving holes on the course being played. Factor that into the decision on who hits the tee ball on the first hole. You want your best driver to be teeing off on as many of the toughest driving holes as possible.
In the Rules of Golf, Foursomes is covered in Rule 29.
Handicap allowances for Foursomes competitions can be found in the USGA Handicap Manual, Section 9-4 (www.usga.com).
Also Known As: Alternate shot, Scotch doubles
Alternate Meaning: Any four golfers playing in the same group (regardless of what format they are playing, and regardless of whether those four are together) in a recreational round of golf is commonly referred to as a "foursome" of golfers.