Button: Small and round, piece of plastic, metal, shell, or other rigid material, sometimes wrapped in fabric or leather that is sewn to the garment so that, through a buttonhole, it is turn on m. 1 - fastened. 2 piece small, generally circular, that is part of some mechanical, electrical and electronic equipment, and to press it or rotate it connects or disconnects all or some of its functions. 3. bud of plants.