A huge THANK YOU to community member Tango for writing up this guide, which was originally posted on r/AmongUs.
Big brain play – This is usually used to describe planned, manipulative, complex plays or investigations. It is also used sarcastically by some players to insult another player's poor logic or reasoning, although this use should be avoided. Opposite of smooth brain or baby brain, which are considered insults.
Call - Another word for sabotage.
Camping – Standing in one place and keeping watch for an extended period of time.
Cap/Capping - Bullshit, bullshitting. See also: No cap.
Common tasks - Tasks that either every crewmember has, or no crewmember has. Getting caught pretending to do a common task that none of the other crew have is one way to get outed as an Impostor.
Clear - Clearing someone means you don't think they could've done a particular kill. You can hard clear someone (confirming someone is crew, and can't be an impostor) and soft clear someone (meaning that this person didn't kill a particular person, or didn't kill anyone in that particular round, but still leaving open the possibility that they could be an Impostor).
Clutch (clutching the game/coming in clutch) - Scoring a win for your team when it's on the verge of defeat. Can apply to both crew and Impostors.
Double kill – Two kills happening at the same time, at the same location.
Faking (tasks) - Pretending to do tasks. As impostor you want to blend in with the crew, and you do this by walking around on the map faking tasks. To accuse someone of faking tasks is to accuse them of being an Impostor.
Fifty-fifty - If two players hard accuse each other for a kill with no other witnesses, it's a safe bet that one of them is an Impostor trying to pin their kill on a crewmate, but you can't be sure which of the two is it. In a 50/50 situation, both players get voted off.
Guarding bodies - Remaining in a spot where you have killed one or more players, with the intent to kill anyone who comes to report.
Hard accuse - Arguing that someone is without a doubt the Impostor.
Hiding bodies – Accusing someone of calling an emergency meeting in order to remove dead bodies from the map, so their location is unknown. "Hiding bodies" also sometimes refers to standing on top of a dead body, so players can't see it.
Imp – Shorthand for Imposter.
Imp strat - Shorthand for "Impostor strategy", accusing someone of engaging in a strategy or pattern of behaviour often done by Impostors.
LFG - Abbreviation of Looking For Group, or Looking For Game.
Marinating - Gaining a crewmember's trust as Impostor by not killing them.
Metagaming – Using out-of-game resources or information to affect in-game decision making. Metagaming is a pretty broad category that includes things that are considered unacceptable everywhere (such as telling your friend outside of the game who killed you, or talking as a ghost during meetings) and things that are generally considered fair game.
No cap - No lie. Used to emphasize honesty.
Pathing - The route you walked during a round (rooms you've been in and how you got there).
Pink warding - Refers to a player standing in a strategic location in order to keep track of player movement, such as the entrance to the drop ship on Polus, or the middle of the Y-intersection on MIRA HQ. It's an uncommonly used term in Among Us. It originated from League of Legends, where players can purchase pink vision wards to place on strategic places on the map.
Pre-jacking (lights) – Camping lights, waiting in front of lights to fix them the moment they are sabotaged
Proxy - Proximity chat, a mod and custom game mode that allows players to talk to each other during the game, with the audio volume being determined by how close or far away players are from each other.
Resetting (kill) cooldown – Calling an emergency meeting to reset the kill cooldown. This is sometimes done at the start of a new game, where the kill cooldown will always be 10 seconds regardless of the lobby's settings. Often considered poor form.
Sab/Sabo – Shorthand for sabotage.
Skip on seven - If you have seven players left with two Impostors, voting out the wrong person means the Impostor are one double kill away from winning. Unless you're sure someone is the Impostor, skipping on seven is good advice to follow, but it's not a hard rule. See also: Vote on six.
Stack kill - A kill that happened when most or all crewmates were crowded around the same spot, making it unlikely that someone saw who made the kill.
Sweaty - A (sometimes derogatory) term to refer to players or lobbies with a highly competitive attitude. The opposite of sweaty is chill.
Sweatlord - A (sometimes derogatory) term to refer to a player with a fiercely competitive attitude. Sweatlords are often highly skilled and experienced, but not always.
Teaming (synonymous with grouping) - Walking together with one or more players during the game, never being alone.
Third impostoring – Intentionally trying to rig the game against the rest of the crew, as crewmate. Examples include knowingly giving false intel, covering for someone who you know is an impostor, or pretending to be an impostor yourself. Crewmates who unintentionally make bad plays or decisions that result in a loss for the crew are sometimes called third impostors as well as an insult, but this should be avoided.
Throwing – Intentionally losing the game. Examples include ratting out your Impostor partner after being caught yourself. Similarly to "third impostor" the term is sometimes used as an insult to bad/losing plays that weren't intentional, but this should be avoided.
Vent kill – A kill that took place on or near a vent, after which the Impostor immediately vented to escape the room or avoid detection.
Vote on six - If a meeting is called with six players and two impostors, you have to vote someone off, or the impostors are one double kill away from winning the game when the next round starts. See also: Skip on seven.