The peloton (from French, literally meaning ball and related to the English word platoon), bunch or pack is the large main group in a road bicycle race.
Riders in a group save energy by riding close (drafting or slipstreaming) near (particularly behind) other riders. The peloton travels as an integrated unit, like birds flying in formation, each rider making slight adjustments in response to the riders around them (particularly the one in front of each).
More loosely, "the peloton" can also refer to professional cyclists in general: "LeMond joined the European peloton at a time when few Americans could."
Merriam-Webster’s Dictionary chose peloton as the seventh place finisher for the Top 10 words of the year 2004.
Riding in the peloton
While only the riders exposed to the wind at the front (and the windward side when there is a significant crosswind) of the peloton are the ones doing most of the work, it is usually advantageous to be positioned closer to the front of the peloton. One reason is to avoid being affected by the elastic band effect in which a change in speed becomes amplified as it propagates to the back of the peloton. The rider riding behind a rider who is changing his/her speed must make the adjustment at a slightly faster rate (due to reaction time) to avoid collisions.
Moreover, being closer to the front means that the rider can react to attacks and changes in position with less effort. Gaps sometimes form in the peloton, and being closer to the front also reduces the risk of getting caught in the rear group when the breaks form. Finally, being at the front of the peloton means dictating the tempo to some degree, and some teams or groups of rider may prefer different speeds as part of their tactics.
The shape or formation of the peloton changes according to many factors. A strong headwind or a hard effort tends to spread-out or string-out the riders, while a slow tempo or tailwind tends to bunch up the peloton into a wider formation. Side wind forces the peloton to form into echelons in the direction of the wind. Often, the width of the road forces the peloton to form into several echelons. When more than one group of riders want to dispute control of the peloton, several lines may form racing one another.