Reactions (SSF4)
Playing a fast paced game like Super Street Fighter 4 can be annoying for someone new to the game, everything is moving so fast and you don't know what's going on. If your a seasoned player then this doesn't effect you as much or maybe not at all, but you can always become better no matter how good you think you are. This page is dedicated to everything veteran players like to call 'Reactions' or reacting to certain things that happen while playing a match.
Reacting refer to your ability to see what your opponent is doing, processing that information and then using it to effectively counter your opponent. This is extremely hard to do because some moves are so fast it is nearly impossible to react to them unless you were expecting it. Reacting to every single thing your opponent does is impossible, but if you react to enough, you can win the round easily. It is a skill to react; training yourself to understand what each character of the game can do and knowing what you and the character you use can do to effectively counter it takes months, but it is a viable skill that is needed to insure that your moving forward with your skill.
This video shows a online player reacting to various moves from different characters, it's a montage of his exploits online but it displays exactly what I'm talking about dealing with reacting to fast moves.
Punishing
'Punishing' is a term that describes the action of countering a move that is 'unsafe.' When you punish someone you are reacting to a move that your opponent did and countering it with your own move. The video above also demonstrates what we would call punishes because the player is reacting to the move their opponent did, countering that move with his own and effectively punishing them for doing that move.
Now I don't want everyone to believe that reacting and punishing is a one way street, if anything it's a 4 lane highway. You can react to your opponent and punish them as well, but they can do the same exact thing to you. Your job as a player is to minimize the opportunities you give them to do these things while maintaining your own reactions. If you can do this effectively your on the highway to becoming a great player.