The queenside a-, b-, and c-files; or the kingside f-, g-, and h-files. Distinguished from the center d-file and e-file. Also called wing.

The files that do not belong to the centre, that is the a, b and c files on the queenside, and the f, g and h files on the kingside. Certain openings that focus on flank development are called "flank openings." Typical first moves for these openings are 1.c4; 1.b3; 1.Nf3; etc.