hot zone

noun
  1. computing a variable area towards the end of a line of text that informs the operator that a decision must be taken as to whether to hyphenate or begin a new line
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