Slipstreaming

Drafting or slipstreaming is a technique where two vehicles or other moving objects are caused to align in a close group reducing the overall effect of drag due to exploiting the lead object's slipstream. Especially when high speeds are involved, as in motor racing and cycling, drafting can significantly reduce the paceline's average energy expenditure required to maintain a certain speed and can also slightly reduce the energy expenditure of the lead vehicle or object.

Drafting is used to reduce wind resistance and is seen most commonly in bicycle racing, car racing, and speedskating, though drafting is occasionally used even in cross-country skiing, downhill skateboarding, and running. Some forms of triathlon allow drafting. Drafting occurs in swimming as well: both in open-water races (occurring in natural bodies of water) and in traditional races in competition pools. In a competition pool a swimmer may hug the lane line that separates them from the swimmer they are abaft of thereby taking advantage of the liquid slipstream in the other swimmer's wake. Drafting also occurs in competitive longboarding.

It is believed, but not yet conclusively proven, that Thoroughbred racing horses draft each other, especially in longer races.

In cycling, any time one bicyclist is riding behind another, energy is conserved, especially at higher speeds.

In road bicycle racing, the main (largest) group of tightly packed cyclists in a race is called a peloton where cyclists ride in a long formation with each (but not the first rider) drafting behind the others before them.

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Wikipedia