Most table tennis players label topspin shots into several categories such as: loop, block or smash. However, modern attacking players have developed an offensive block called an active block. Active blocking is a combination between a block, loop and counter loop. It is best used off-the-bounce against a slow to medium speed loop.
Watch in this http://www.youtube.com/watch?v=kwbcgOPxx8w&feature=fvsr as Kenta effectively uses active blocking to stop his opponents’ attack and take control of the table.