The high jump is an athletics event where competitors must jump over a bar at measured heights.
In modern high jump, a fibreglass or aluminium bar (other materials allowed, but weight and sag parameters are controlled by rules) of approximately 4 metres in length (IAAF rules control length for record purposes), with a round (or triangular or square) cross-section for most of its length but with two square resting points at each end, is placed at a measured height on two "uprights" which allow the bar to rest on its ends at a measured height; cleared heights are reported by measuring the altitude of the top of lowest part of the bar). Directly behind the bar is a soft foam mat (or any other safe landing material) that allows a comfortable and safe landing. Competitors run up (standing start is allowed) to the bar and must leap, off one foot, and clear the bar. They may touch the bar in their clearance, but if the bar falls due to their touch then the jump is unsuccessful.
Historically, a variety of techniques have been used by competitors to clear the bar, but since its popularized exhibition (very well may have been used earlier) in the 1968 Summer Olympics, Dick Fosbury won a gold medal in the high jump. His method was to sprint diagonally towards the bar, then curve and leap backwards over the bar. This method was then called the 'Fosbury Flop' and has been almost universal amongst elite competitors, though dive straddle biomechanically competes favorably with the flop depending on body structures and other factors.
In a competition, the bar is intially set at a low height, and is only moved upwards in set increments (usually 3 or 5 centimetres). Each competitor has the option of choosing what height they wish to start at, but once a height has been cleared by one competitor obviously a competitor cannot choose to start at a lower height. Once a competitor has elected to start jumping, they can choose whether to attempt subsequent heights, but if they choose not to attempt a height it counts as a "pass". Any competitor who records three consecutive misses is out of the competition. The competitor who clears the highest jump is declared the winner. If two or more competitors clear the same maximum height, the competitor with the lowest number of failed attempts (at any height). If that fails to break a tie for first place, then a jump off is conducted; heights obtained in such a jump off are eligible for records. IAAF rules are nearly universally the model used for sport high jumping.