A DIP switch is an array of tiny little switches put together in a standard Dual In-line Package (DIP). It is used on PCBs to customized the behavior of electronic devices in specific situation. Each switch has two possible state - ON and OFF. A DIP switch is an alternative to a jumper block. It is quicker to change and have no parts to lose.

This is a slide type of DIP switch with Single Pole Single Throw (SPST) contacts. The distance between each adjacent contact is 2.54mm making it breadboard friendly. A slide to the position ON closes the contact. You can interpret each switch as having one bit binary value or you can interpret the values of all switches as one number. For example an 8 switches can give you 256 combinations which can represent a byte.

DIP switches were used in old PC motherboards and expansion cards before software configuration took over. You can still find them in automatic gate remote controls as a mean to set different radio frequency for different gate.