a small disk or knob sewn onto a garment, either to fasten it by being pushed through a slit made for the purpose, or for decoration.
a blouse with five buttons in front
a knob on a piece of electrical or electronic equipment that is pressed to operate it.
She pushed the button and waited in front of one of the shiny gold colored doors.
a badge bearing a design or slogan and pinned to the clothing.
You can't see from here, but those badges and buttons sport a plethora of pro-life phrases.