A switch is a device for making or breaking an electric circuit, or for selecting between multiple circuits.

In the simplest case, a switch has two pieces of metal called contacts that touch to make a circuit, and separate to break the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working. Sometimes the contacts are plated with noble metals. They may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as conductive plastic, are sometimes used. The moving part that applies the operating force to the contacts is called the actuator, and may be a toggle or dolly, a rocker, a push-button or any type of mechanical linkage

A DPDT switch has six connections, but since polarity reversal is a very common usage of DPDT switches, some variations of the DPDT switch are internally wired specifically for polarity reversal. They only have four terminals rather than six. Two of the terminals are inputs and two are outputs. When connected to a battery or other DC source, the 4-way switch selects from either normal or reversed polarity. Intermediate switches are also an important part of multiway switching systems with more than two switches (see next section).

A KVM switch (with KVM being an acronym for Keyboard, Video, Mouse) is a hardware device that allows a user to control multiple computers from a single keyboard, video monitor and mouse. Although multiple computers are connected to the KVM, only one can be controlled at a time. Modern devices have also added the ability to share USB devices and speakers with multiple computers.

A user connects a monitor, keyboard, and mouse to the KVM device, then uses special cables to connect the KVM device to the computers. Control is switched from one computer to another by the use of buttons on the KVM device, with the KVM passing the signals between the computers and the keyboard, mouse and monitor depending on which computer is currently selected. Most devices also allow control to be switched through keyboard commands (such as hitting a certain key, often Scroll Lock, rapidly two or three times). Some KVM devices also send signals to the computers that are not currently selected to ensure that they do not think that the keyboard, mouse and monitor are dis-connected.

other widely used switch

KVM Switch
Pressure switch
Network switch
Micro switch