A hat-trick occurs in cricket when a bowler dismisses three batsman with consecutive deliveries. Hat-tricks are very rare and as such are treasured by bowlers. The term was first used to describe HH Stephenson's feat in 1858 and was used in print for the first time in 1878.
Taking two wickets in two consecutive deliveries is occasionally known as a brace, or (more commonly) being on a hat-trick. This is only a run-up to the hat-trick. If a hat-trick is not achieved, it is not called a brace.
Four wickets in four balls is referred to in cricket literature and record books as four in four but the term double hat-trick has also been used in the media, as it will contain two different sets of three consecutively dismissed batsmen.