Jack and Jill is a format of competition in partner dancing, where the competing couples are the result of random matching of leaders and followers.
The name and format were created by Jack Carey at Hank & Stans in Norwalk, California in the early 1950s to encourage a variety of dancers to enter competitions.
[1][2] The gender-ambiguous term Pat and Chris has been used, particularly in LGBT dance venues, to refer to events where the gender of lead and follow isn't specified.
Thus, the winner is largely decided by luck of the draw, with the winning couple often being regular dance partners who were lucky enough to be paired together.
Depending on rules specific to the event/competition, a Jack & Jill competitor may or may not be allowed to dance with their regular competition partner (one that they compete with in a choreographed division).