These are all generic terms to describe a component whose spring loaded tip will provide a reliable electrical contact to a target whose distance away may well be indeterminate. The traditional use for them is to make contact with printed circuit boards (PCBs) or electrical components, in order to test functionality and to measure the value of the components. They are widely used in vacuum test fixtures associated with automatic test equipment (ATE). They are also used inside a functional test station as part of a larger production line.
The test probe is comprised of a metal tube, ready assembled with a spring and contact plunger, supplied as a one-piece item. They are usually gold plated as gold is an excellent electrical conductor and is resistant to corrosion. The electrical cable is generally connected to a receptacle which the test probe inserts into. The use of a receptacle allows the test probe to be removed for cleaning or replacement without having to disconnect the electrical cable (see illustration below).