What is carpet texture retention

We bought a new house in 2005. Allegedly, we got upgraded carpet. I say allegedly because we paid for better carpet but this stuff has looked awful for quite some time. I often wonder if we got builder's grade and not what we paid for. It looks worn, squashed, frayed and stains easily. This could maybe be expected in the family room but we walk on the carpet rarely in our bedroom and even it looks awful. I have often seen references in postings to warranties for a carpet's texture retention and was wondering what that is and how that differs from the carpet warranty. The carpet needs replaced and before we fork over great bucks I figured I better see if it can be salvaged under our warranty or if not what I need to look for in the replacement. Thanks!