V.V.V.V.V. said:
Post-thrash = thrash paced/thrash inflected metal with leanings towards other (more complex) genres as well, usually progressive metal/prog music in general...
Generally post anything = taking the basic archetype of the genre after the prefix and adding in other influences, while still retaining enough of the post-prefix genre to interest most (non-purist) fans of said genre. Post-rock is a good example: it takes elements of rock and adds elements of ambient, electronic music, atypical jazz structures, and sometimes even classical composition to the music. Post-black as well: progressive/electronic/ambient/experimental-influenced black metal in general...
The new Textures album is fucking awesome post-thrash/-core/progressive metal with some post-rock influences. It's way better than their debut IMO.