s-foil

Ah, the S-foil. The S-foil is a piece of technology in the Star Wars Universe designed to permit a spacecraft to change shape, allowing guns and hyperdrives to work more efficiently. In Role-playing games the S-foil is an attribute which some vehicles can have, depending on the game. Usually, X-Wings and B-Wings can have s-foil attributes. According to http://www.theforce.net/swenc/encyc-s1.htm :

the wing assembly of an X-wing. The wings are connected diagonally, and when the S-foil is moved into attack position, the opposing wings spread apart. On an X-Wing, this results in the characteristic X-shaped wing pattern. On a B-Wing, it brings the wings upward to form the well-known cross-shape wing pattern. The name S-foil is a shortened term for Strike Foil, the original name used to describe these wings by Incom Industries.