Some sources suggest that the letters "LT" found on the back of a Chevy vehicle stand for "Luxury Touring". The "Z" doesn't appear to be an abbreviation for anything, but when tacked onto the end of "LT" it means that the vehicle is considered to be the "top of the line" or the "high-end luxury" version.
Overall, "LTZ" just lets buyers know that a vehicle comes equipped with all of the standard and optional features available for the model. For example, the 2014 Chevy Silverado 1500 LTZ comes with a trailering package and automatic locking rear differential, but the LT version does not.
According to The Verge, apart from the engine, wheels, seats, and enormous difference in size, 2015 Chevys will be nearly indistinguishable from smartphones! Find out more here.