Buttons are small hard objects sewn on to shirts, coats, or other pieces of clothing. You fasten the clothing by pushing the buttons through holes called buttonholes.

If you button a shirt, coat, or other piece of clothing, you fasten it by pushing its buttons through the buttonholes.

A button is a small object on a machine or electrical device that you press in order to operate it.

A button is a small piece of metal or plastic which you wear in order to show that you support a particular movement, organization, or person. You fasten a button to your clothes with a pin.

If you say that someone presses the right button or pushes the right button, you mean that they get what they want from a particular situation or person by behaving in a clever way.