A file is usually a metalwork tool. Unlike a woodworking file which is called a rasp, where the teeth are set very wide apart, a rasp has teeth set much nearer to each other and running diagnally across the blade. The teeth are also shallower. This leads to a much finer cut (called planing) and allows for material to be planed down to a very smooth finish.
Metal files, are designed to cut or plane on the stroke away from the body. Using a file in both directions will eventually spoil the teeth. Rasps and Files can be bought in a few shapes.
Files can be flat on both sides, flat on one side and half-round on the other, completely round or triangular. These shapes allow for most types of shaping to be done with a rasp before the work is finished using finer tools.
See also our project on using rasps.