TTL

abbreviation for

transistor transistor logic: a method of constructing electronic logic circuits
through-the-lens: denoting a system of light metering in cameras

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