A clicker is any device that makes a clicking sound, usually when deliberately activated by its user.
For example, the clickers used in clicker training are small hand-held devices that make a loud and consistent sound to assist in training animals. They usually consist of a piece of thin metal held in a casing so that the metal is slightly torqued; depressing one end of the metal causes it to pop out of alignment and releasing it causes it to pop back into alignment, each time making a sharp click.
With some clickers, the user depresses the metal directly with thumb or finger; with others, a button extends above the surface of the casing so that depressing the button makes the metal click.
A clicker is also what some people call a remote control.
