The goal of this thread is to define the current terminology used by competitive players. We often say phrases and words that we take for granted, but other players don't know what we're talking about. Hopefully, this thread proves to be a good resource for newer players to know and understand commonly used phrases.
A good starting place is Jexik's
Common Abbreviations. This is meant to add a lot of the more modern terminology to an already-excellent list.
Unit Terms
Bruiser: a unit that consistently throws 4-5 attack dice. Examples include Horned Skull Brutes, Tandros Kreel, and 1 squad of Knights of Weston with Finn.
Can-Opener: a unit that consistently throws 6+ attack dice. This allows them to pretty consistently have a chance against a Major Q9. Examples include Nilfheim, Eltahale, and the Frost Giant.
Splash: using (generally) no more than 150 points or 9 hexes of a single common unit. Common examples include 1-2x Mezzos, 2x PKs, and 1-2x HSBs.
Tech: a unit (often times a splash) that specifically targets one particular matchup/group of matchups, often time done to cover a weakness in your army. Examples of anti-range tech are 1-2x PKs and Krav.
Army Terms
Bread and Butter: typical army with simple OM management and multiples of 1-2 common units.
Splash: an army (generally for RtW) that uses a variety of splashed units alongside Raelin. These armies are generally defensive with a pod-like nature to them. Generally has units that fill the roles of Screen, Range, and Bruiser, as well as sometimes having Anti-Range.
Toolbox: different from Splash armies in how they play because of their lack of Raelin. Toolbox armies utilize individual splashed pieces that are all threats yet defensive enough by themselves to afford not having to spend 80 points on Raelin. Worth separating because these armies play very differently than a typical Splash army. Chosen units in these tend to fill multiple roles as opposed to a single one (examples: Arkmer and Tandros are both Bruisers and Screens, PKs with Concan are Bruisers and Anti-Range). Threat Sequencing is very important for Toolbox armies, more so than Splash armies that like to have all of their pieces up at least somewhat.
Other General Terms
Kiting: shooting from maximum range of a unit and using your move to maintain maximum distance at all times. Often, it is better to kite with a unit like Nilfheim and get only one shot off while remaining protected rather than rushing in to get off his melee attack or 3x4 and exposing him to counter-attacks. One of the biggest mistakes I see less experienced players make is not effectively kiting. Units that kite well are very mobile with good range. Examples include Krav/Skahen, Nilfheim, and Mimring.
AxB (at C): a common abbreviation where you are making A (number of attacks) with B (amount of red dice) at C (the maximum range). For example, Kaemon's and Q10's specials are generally called 2x4s, 4th Mass make 4x3s at 6, etc.
Threat Sequencing: the order in which you deploy your army pieces across the board so that they best line up into your opponent's likely line of play (thanks vegie!). Find comparative advantages between your armies and make sure you get the matchups within the armies that you like.
Tether: tying up an opponent's figure to prevent it from moving and attacking more important figures. A vital part of successfully playing melee armies is putting a squaddie in a normally sub-optimal tactical position to prevent them from engaging or shooting your more important figures.
This will be a progressive list as I think of more things that should be added. As always, please leave feedback, and happy Scaping!