Well, there are a lot of terms, I'll just explain some of the "popular" ones.
Walls have very high defense. They are usually used to block physical moves.
Sweepers try to quickly knock out ("sweep") the opponents Pokemon. They have high Speed and Offensive stats.
A Pokemon that can take hits, and fight back, like a a "tank"
Like a tank, a Staller takes hits and fights back. It stalls.
More info on the terms