There are theories about it being derived from pre-Christian fertility rites, being based on 'Moorish' dances which spread up through Spain into Europe in Medieval times, being a rustic version of the dances of the Tudor court, or being attributed to the troubadours of the Middle Ages.
Nobody knows for sure.
It is characterised by the predominantly white clothing, bells tied around the shins, and white hankies or sticks held in the hands. Generally the dances are scored for six, although a Morris jig is usually danced by either one or two, and remain within a limited patch of ground. Simpler forms of the Morris dance are used by the 'Molly' dancers of East Anglia and the Christmastime Morris dancers of the border area between England and Wales. The girls' Carnival Morris is a 20th century off-shoot of the men's North West Morris. It has developed its own format and has continued to evolve, as seen in the 'Entertainers' sections of their competitions.