Fighting games have so many terms. For me I just kinda picked up on what they meant, you usually can infer. But for some people it may be different so don't stress it. I gotchu bro, i ripped some of these from reddit sooooooooooooooo yea. These are probably some of the most common. A great resource for shit I didn't say here.

Cancel: Breaking out of a current animation or move by inputting another move that cancels the previous one.

Hit Confirm: The act of waiting to see if an attack lands, then reacting by continuing into a combo or special attack.

Footsies: The mid-range ground-based aspect of fighting game strategy. It refers to a situation where both players are outside of combo range and attack each other with mid- or long-range, generally safe attacks (pokes). The ultimate goal is to control the flow of the match, bait the opponent into committing errors, and attempt to punish mistakes.

Knockdown: Refers to a character's downed state that occurs when struck by some attacks.

Juggle: A combo in which the victim is hit multiple times in midair. The move used to start the juggle is called a launcher.

Neutral: The situation where neither opponent is attacking or defending, for example at the start of the game.

Poke: A quick attack that is done to hit an opponent from a short distance away to keep the attacker safe.

Pressure: Using a sequence of attacks to keep an opponent on the defensive.

Punish: Attacking an opponent who is recovering from performing an attack.

Whiff: A move that misses the opponent completely.

Safe: A move that cannot be punished if blocked.

Dp: Short for dragon punch, used for a move that is an anti air that invicinble on start up.

Anti air: attack that knocks opponent out of the air.

Lab/Labbing: going into training mode and practicing

Mixups: A situation where the offensive player has several ways to attack that each require a different defensive action to stop

Set: a groups of games, usually Ft2 or Ft3

Ft: "First to", first to 3 is whoever reaches 3 game wins won.
Zoning: The act of using long-range attacks to try and prevent your opponent from coming closer, typically by using long-distance normals, fireballs, and backwards movement.
Skill Check: Sink or swim, maybe a mechanic or certain character that checks your skill to see if you really all that or not.