What is a bracelet designed to protect electronics from an electrostatic discharge by preventing a buildup of static electricity?

The copper bracelet, worn on the wrist, is connected by a cable to an earthed source. The earth source can be the earth socket on a mains electrical 3 pin socket, or attached to a cold water pipe, or to a water radiator, etc. The idea is that any static electricity that builds up in a person, is dissipated safely to earth along the cable. This prevents delicate computer components being damaged should a spark of static jump from a person to the components on the motherboard.