Abbreviation for One Character Victory. It is used when a player wins a match in a team fighting game (KoF, Tekken Tag Tournament, DBFZ, Marvel vs Capcom...) using a single character. As characters do not regain life by knocking out an opponent, these victories are usually overwhelming.
Okizeme (literally wake-up attack in Japanese) is the art of pressing an opponent to the ground, or to his feet. This is usually done by putting him in a situation where he must immediately block, often with a new attack sequence or a projectile. This type of technique is much more prevalent in 3D games, which generally allow for an attack on an opponent on the ground, which is uncommon in 2D games. In the latter, an opponent on the ground cannot usually be attacked, and can get up by countering or blocking any attack (provided he chooses the right option), making okizeme a more psychological concept, known as a Wake-Up game. This is not true for all 2D games, such as in the BlazBlue series where an opponent can get up by rolling in multiple directions. Knowing how to press an opponent who is getting up (as well as anticipating which direction they will go) can have a decisive effect on the final outcome of a match.
A situation where a player's action is ambiguous, and the game program itself will determine the outcome based on the situation. Usually the game chooses the best possible outcome for the player who performed the action. For example, in Virtua Fighter 3 it was possible to do the same action to block a move and make a catch, so the game would throw a catch if it could pass, or just block if the catch could fail. In SNK vs. Capcom: Chaos, attempting an air grab resulted in a light hit if no opponent was in range. Finally, in Street Fighter II, a hold made with a Negative Edge will throw the opponent if he is in range, and do nothing if he is not, allowing a non-punishable grab attempt. The select option is sometimes the result of a flaw or overlooked mechanic in the game.
Orientation is one of the laws of Focal Adherence, forcing all attacks, defences and moves to relate specifically to the opponent's position, while dictating the direction each player faces. This law prevents a character on the left side of the screen from turning and running to the left when the player presses that direction. If characters reverse their positions, the orientation forces them to turn and face each other automatically, or when a player tries to start another action after switching sides. This law implies that the terms "left" and "right" no longer have much meaning in a fighting game - it is better to talk about "front" or "back", depending on whether you are moving towards or away from your opponent. Although most fighting games work this way, a few games do not use this mechanic, such as Super Smash Bros. Melee.
A condition meaning that an opponent has been knocked down. An OTG attack is an attack that hits an opponent on the ground.
A blow that breaks the low guard, only the high guard can protect against it. The term is more commonly used to designate a ground strike, as all air strikes are already over-head, so there is little point in pointing this out.