From Shoryuken Wiki, Marvel vs. Capcom 3 Strategy and More!
Hit and Block Stun
Two terms will be used a lot in this guide: Hit Stun and Block Stun. Those of you playing Street Fighter are well aware that the game is all about hitting the opponent right?
Well, if you notice, whenever you land an attack on the opponent, the opponent gets "stuck" in a state. When you hit them, they go into an animation of reeling from getting hit. When they block your attack, they get stuck in a blocking pose for a fixed amount of time.
These are what are referred to as Hit Stun and Block Stun. Hit Stun is the concept that, when hit, you are stuck in the reel animation for a while. Any hits that connect during your Hit Stun are considered a hit that combos on you. And Block Stun is the concept that, when you block an attack, you are stuck in the block pose for a while. Any attack that connects on you during Block Stun is considered a true Block String. These are very important concepts to know about, and they will be talked about a lot throughout this guide.