What is a gremlin?

In folklore, a gremlin is a small, mischievous creature that is said to cause problems or damage to machinery, especially aircraft. The term gremlin is often used to describe a hidden problem or fault in a machine. The word gremlin is derived from the Old English word "gremian", which means "to trouble" or "to irritate". Gremlins are often depicted as small, furry creatures with large ears, sharp teeth, and claws. They are said to be very clever and cunning, and they enjoy causing trouble. Gremlins are also said to be very nocturnal, and they are most active at night.