proper time

noun
  1. time measured by a clock that has the same motion as the observer. Any clock in motion relative to the observer, or in a different gravitational field, will not, according to the theory of relativity, measure proper time
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