1.) the rows of holes between stamps that enable easy separation of stamps. The gauge (perforation size) has frequently changed. For example, perf 15 was introduced in 1857, perf 12 in 1861, perf 10 in 1914, and perf 11 in 1917. Other perfs have also been used. "Perf" is a common contraction for perforation. 2.) the holes that were privately added by some private companies to help coil stamps pass through a machine.