The windscreen wiper motor is an electric motor that powers the windscreen wipers. They generally are able to move the wipers at varying speeds. Wiper motors use clever gearing technology to transfer the power to the wipers. They can last for a long time powering well over 1 million wipes of the windscreen.
A worn out wiper motor will often cause the wipers to work less effectively at removing water from the windscreen, it can also cause the wipers to work more slowly or at an erratic rate.