No, it means the worst case is bounded above and below by n^2. That is, the worst-case scales no worse or better than n^2, but approximately proportional, asymptotically. (Whereas, for example, every O(n^2) algorithm also happens to be O(2^n))
The best case is something entirely separate, and can itself be bounded from above or below.
The best case is something entirely separate, and can itself be bounded from above or below.