A form is a sequence of movements traditionally used in the practice and performance of a martial art. By practicing a form over and over again, it is hoped that in time the practitioner will be able to execute those movements in a natural and reflex-like manner.
Most martial arts don't use the English word "form" in their teachings. Instead they use a word from the country where the art originated.
Note that these tags should not be used. Use the more generic "forms" tag instead.