Jumpers are usually covered with a plastic layer that serves as electrical insulation and provides protection against contact. It also prevents electrostatic discharges from damaging highly sensitive electronic components.
Jumpers are used for fixed configurations of hardware components by plugging them onto the corresponding pin pairs of a pin row. For example, two points of an electronic circuit can be connected, hard disks can be configured, memory areas can be switched or certain operating states can be defined.
The position at which the jumpers have to be plugged in can be found in the respective operating instructions.