An update to the Left 4 Dead Blog offers 12 terms from the Left 4 Dead Dictionary, which makes me personally proud as a descendant of Noah Webster that survivors of a zombie apocalypse would take the time to consider etymology as well as ammo supplies. All kidding aside, the dozen terms they offer are actually Valve's shorthand for discussing level design. Word is: "Internally, when we are in the early design stages of a campaign, we need an easy way to discuss the design without having to constantly consult drawings or rough maps. To do this, we created the Left 4 Dictionary. The dictionary is a set of terms used to describe a space."