This is terminology that applies to the Marvel vs. Capcom series, among other fighting games. It consists of playstyle definitions, attack types, attack movements and so on.
+ Command Normals: Command Normal's are moves which are made with a direction plus a attack button. These can have a number of purposes, like projectiles or stronger normals. These are shown in the command list in red in Ultimate Marvel vs Capcom 3. They are not listed in the oringinal Marvel vs Capcom 3.
+ Special Moves: Special Moves are created by a motion on your stick plus a attack button. They all of different properties so you need to figure out which one does. They show up in green in the command list in both versions of Marvel vs Capcom 3.
+ Hyper Combo: These are created by a motion and two attack buttoms, they are very strong moves that can create massive damage. They cost one meter of super level. They show up as blue in both versions of the game.
+ Grab/Throw: Grabs or Throws are made with forward or backward heavy attack. They throw the enemy in the direction your stick is facing, its good for getting out or getting the enemy in the corner. These are also can be made in the air which are called + Air Grab/Throw.
OTG/Off The Ground: An attack that can pick the enemy off the ground to extend your current combo. These attacks can be made by your current character or with certain asists.
Overhead: Overheads are attacks on the ground that can hit enemies who are crouch blocking. It has the same properties as a jumping attack.
Mix-Up: Mix Ups are hard to block moves that can make the enemy vulnerable to further attacks and combos. They are usually done with an assist. They generally involve hitting high then low.
Crumple: A move that causes a crumple state leaves the opponent completely defenseless and unable to move for a short period.
Hard Knockdown: A move that leaves the opponent lying on the ground for a certain amount of time. This time varies depending on the move used. The opponent can be hit with OTG moves.
Soft Knockdown: A move that causes the opponent to roll once they hit the ground. However, they take a long time to land. Therefore, the opponent can be juggled. If high enough, they can recover in the air depending on the move.
Ground Bounce: A move that causes the opponent to bounce from the floor, allowing combo extensions. They may either enter hard or soft knockdown once they hit the ground, depending on the move used.
Wall Bounce: A move that causes the opponent to bounce off the walls, allowing combo extensions. They may either enter hard or soft knockdown once they hit the ground, depending on the move used.
Strike: A move that allows the opponent to recover in the air. This is mainly used for reset setups.
Mashable: A move that is mashable will cause extra damage if the attack button is hit multiple times during the move, a.k.a. mashing.
Happy Birthday; A move that catches two of the oppposing characters in a combo. Catching all three characters in that combo results in a Merry Christmas.
Note that all directional instructions are as if for a character facing to the right side of the screen.
QCF/Quarter Circle Forward/Hadoken Motion: These moves are performed by pushing down and sliding it to the right.
QCB/Quarter Circle Backward: This motion is done identically to the one above but mirrored such that you slide to the left, instead.
Tiger Uppercut/Shoryuken Motion: This motion is done by pushing right, sliding in down, and then down-right quickly.
Backward Tiger Uppercut/Shoryuken: the reversal of previously mentioned.
HCB/Half Circle Back: This is a motion usually used by special grabs or hyper grabs (also called Command Grabs). This is done by pushing the stick right and then moving though a semicircle, through down, to the left.
HCF/Half Circle Forward: A mirror of the above move, where you initially push left then do a downward semicircle to the right.
Tiger Knee: While not actualy a command, it is done by jumping and doing the command very fast so you do it right above the ground.