tactical voting


noun
  1. (in an election) the practice of casting one's vote not for the party of one's choice but for the second strongest contender in order to defeat the likeliest winner

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012