A whip is a member of a political party in a legislature whose task is to ensure that members of the party attend and vote as the party leadership desires. The term originated in the Parliament of the United Kingdom and derives from the hunting term “whipper-in,” i.e., preventing hounds from wandering away from the pack.
Whip is also used to mean the voting instructions issued to members by the Whip.
The Whip for each party is an elected position, responsible for knowing how each member of his or her party will vote, and attempting to change votes in order to bring everyone possible within the party line.
Official party whips are almost exclusively found in larger “big church” parties where the distance between members on the parties’ right and left wings may be significant, which in turn can easily lead to internal rebellion against the official party view when certain issues are voted on.