I still don't understand what it means
it's the bodystyle or generational reference to specific years.
you may be led to believe that gmc, chevrolet, cadillac are all different.... they are but only on the outer shell
under the skin they are ALL THE SAME for the most part.
so for instance 2000-2006 are commonly referred to as "new body style" NBS for short.
the same generation is also referred to as GMT800, which is generally a 00-06 1500 4.8L, 5.3L, 6.0L
there is more to it based on years for instance 00-01 was a crossover year where gm made BOTH obs & nbs
then in 07 they made some pickups nbs & nnbs, the pickups silverado/sierra are the same as the suv's in a multitude of ways also.(yet, yes they are pickups)
if you stick around and read and learn you will get a better understanding of the specific differences as well as the similarities