instruction to MP to attend vote: a notice, underlined three times for emphasis, issued to members of a political party requiring them to attend and vote in a particular way on a specific motion in the British Parliament
http://encarta.msn.com/encnet/features/diction ary/DictionaryResults.aspx?refid=561508751
noun (in the UK) a written notice, underlined three times to stress its urgency, to members of a political party to attend a parliamentary vote.
http://www.askoxford.com/concise_oed/threeline whip?view=uk
A member of a legislature appointed to facilitate party organization within the legislature. Generally, parties will each appoint a chief whip with a team of junior whips. The term is derived from the �whipper in� of English hunting parlance, whose role it is to keep the pack together in chasing its quarry. In the UK House of Commons the whips' intentions are made clear by the weekly circulation of a document detailing important votes, "three" lines being scratched under an item indicating the whips' strongest call for support. In many legislatures the job of the whips has expanded to take some responsibility for the management of the legislative timetable itself, as well as facilitating the communication of views between party leaders and back-bench representatives. Whips also become the means through which opposing parties can communicate over the management of the work of the legislature. In the UK House of Commons this is known as the �usual channels�.