Static
Static electricity is a naturally occurring form of electricity that is created when objects are in motion.
When a static charge is built up, typically contact with a conductor results in an electrostatic discharge (ESD) (aka shock).
The shock occurs because of the different potentials between the charged object and the conductor.
The shock flows through the object to ground thereby reducing the potential to zero.
People and electronic equipment can build up a static charge.
ESD can destroy equipment. Good grounding helps prevent ESD damage.