Conventions
Any group of people engaged in a group activity will, over time, develop its own shorthand and quirks. Archers talk about form, draw weight, draw length, optics, arrow flight speed, and lots of bow-related things that don't really have any use outside of that context. Computer types can have entire conversations only tangentially related to English at all. Larps are no different.
In this case, we have a number of game conventions that everyone just sort of seems to know without ever really having been told. We pick it up from each other and pass it along by example to new arrivals. It's not ideal and it contributes some avoidable length to the learning curve. In the interest of easing that transition, these are some of the things that are common in the game and useless out of that context.
Common Conventions:
Counted Actions: Counted actions exist, loosely, to handle two conditions. One, you want to do something that's perfectly viable for your character but out of the question for you. If your character has Wings, for example, they're free to leave the ground, but you probably can't sprout your own wings and fly. Two, you need to take some specific action for which rules provide a fixed delay - refitting your armor, for example, takes sixty seconds and it technically a sort of sixty count. Binding Strike is counted to let you know how long you have before you get eaten or whatever. Killing Blow takes a three count which sounds fast and it is if no one's trying to stop you. However you arrive there, all counted actions work the same way: You start at the end, announce what you're doing and the top of the count, then count down, repeating the announcement until you finish at "I whatever 1", at which point your action is completed and everyone should react accordingly. You may see this a lot on modules, where Marshals have to handle player actions we didn't expect - it's easier and smoother to assign a count than call a meeting of the Rules Team and argue about it.
Out-of-Game: A character that's out of game is neither affected by nor can affect the state of the game world. Ideally this is indicated by a white headband - some people (like Plot) spend more time out of game than in, running modules and overseeing stuff. If you're less commonly out of game, or just need a quick minute to retie your boots, putting your hand or your weapon on your head is accepted shorthand for "briefly out of game".
Reps: You'll see this a lot in the rules and you'll hear it a good bit on site. A rep is a physical representation of an in-game item. "Physical representation" being unwieldy and people being people, this was inevitably shortened to "physrep", which you'll still hear from time to time, and then "rep", which you'll hear a lot. Your boffer long sword is a rep for an in-game long sword. Your armor rep is whatever you wear around to justify using armor points when you get hit. It sounds pretty self-explanatory and for the most part it is, but there are some murky areas, too. Spell packets can, variously, be reps for poison vials, thrown weapons, or literally nothing (for mages and other spellslingers.) Reps have a necessary but not tightly-coupled association with...
Item Tags: These are the out-of-game indicators of in-game possessions. You can have a beautifully constructed boffer sword, but you can't actually use in the course of the game without a corresponding item tag for it. Lots of tags come attached to reps. Some are just tags - very few people bother with reps for their poison stashes beyond the packets they intend to throw at people.