noun - A slipstream is a region behind a moving object (e.g., open water swimmer) in which a wake of fluid (typically air or water) is moving at velocities comparable to the moving object, relative to the ambient fluid through which the object is moving. Slipstreaming or drafting works because of the relative motion of the fluid in the slipstream.
Slipstreaming is to swim close behind, or slightly to the side, usually somewhere between the hips and ankles, of another open water swimmer (or swimmers) in order to take advantage of the faster moving water, especially in a race.
The cagey veteran was slipstreaming behind the young swimmer throughout the race.
hang on, follow, drag and free ride, drafting