Slipstreaming is a technique used, especially by cyclists, to take advantage of the airflow around fast-moving objects in an effort to reduce drag. As a high-speed vehicle travels forwards it encounters air resistance, or drag, which works against the direction of travel.
Cyclists racing in a velodrome travel as fast as possible, but the faster the bike goes the greater the drag. To combat this, two or more cyclists can slipstream, or draft. It all comes down to aerodynamics of an object through a fluid (note: gases, like air, are referred to as fluids).
The lead cyclist in a race pushes through the air ahead of them, which diverts the air stream around the sides of the bike. This disturbance in the airflow creates turbulence and a pocket of reduced or negative air pressure in the wake of the bicycle. This area of lower pressure (a partial vacuum) is the slipstream and a cyclist pedalling in this region requires less effort as they encounter less drag, and in some cases they will even experience forward suction.