A button is a small, flat, round object often found on clothing. It can also describe the round disc you press to turn on an electronic device, like the button you push to turn on your computer.
The noun button also can refer to the little round billboards people pin to their clothes to display their favorite political candidate, band, organization, or saying. Button can also be a verb, which describes the act of fastening buttons, like when you button your shirt. Or if you work at an electronics factory, your job might be to button, or attach buttons to, a cell phone.