Button

Small, usually round, fasteners used to attach two pieces of fabric together. Traditional type is composed of two parts: a short nail that is attached to the fabric, and the more visible part, the head.

Typically made of a metal alloy such as copper, brass or aluminium. Three styles can be distinguished: shank, sew-through and stud.

Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary