The words switch are interpreted as open and closed. It also refers to an electronic component that can open a circuit, interrupt current flow or make it flow to other circuits. The most common switch is an electromechanical device that is operated by a person, with one or more electronic contacts. The "closed" of the contact indicates that the electronic contact is on, allowing the current to flow; The "open" of the switch means that the electronic contact is not conductive to form an open circuit, and no current is allowed to flow. Classification according to use: fluctuation switch, band switch, recording and playing switch, power switch, preselection switch, limit switch, control switch, transfer switch, disconnector, travel switch, wall switch, intelligent fire switch, etc. Classification according to structure: microswitch, ship type switch, button switch, toggle switch, button switch, key switch, as well as fashionable membrane switch and point switch. Classification according to contact type: switches can be divided into three types according to contact type: a type contact, b type contact and c type contact. The contact type refers to the relationship between the operating condition of "the contact closes after operating (pressing) the switch" and the contact state. The switch with appropriate contact type shall be selected according to the application.