In its original meaning with metal type, a kern meant having a letter stick out beyond the metal slug to which it was attached, or it cut off part of the body of the slug to allow (other similarly-trimmed) letters to overlap. A kern could therefore bring letters only closer together (negative spacing), but it was possible to add space between letters. Digital kerning could go in either direction. Tracking can similarly go in either direction, but with metal type, one could make groups of letters only farther apart (positive spacing).