Here is a list of those terms people will have difficulties understanding; this will be expanded while writing and difficult words will be added to this list as the book grows. The following are some basic words:

Alpha Shadows
A technique for lighting in a map that results in controlled shadows in the finished map. Typically, it is used to project shadows through textures such as grates or glass that are partially or mostly transparent, simulating realistic shadowing on the receiving surface.
An areaportal is a type of brush, defined by using the system/areaportal texture. Areaportals are most commonly used in doors. They block the -VIS process ingame, meaning your computer does not draw what is behind the areaportal. When the door containing the areaportal is triggered, it tells your computer to render and draw the room behind the areaportal. This is a very common, simple, and effective technique to improve FPS in a map.
The basic building block of GTKRadiant. It is used primarily to define the physical structure of the area being designed. The term brush is used by GTK to refer to anything that is not an entity, and therefore also encompasses patch meshes. A brush can be made to represent anything from solid matter (metal, dirt, wood, etc.) to liquids (lava, water, etc.) to gases (fogs), depending on the textures and shaders applied to them.
A System shader designed to 'caulk' or seal a map. In-game, it is a transparent solid texture. It is best applied to all surfaces which a player will be unable to see while in-game.
The Clipper Tool is used to clip (IE, cut away) parts of a brush in order to alter it's shape. This is generally used to turn a standard 6 sided brush into a brush with fewer or more sides, depending on what is required for it's placement. It has two versions; two-point clip cuts along a single plane, and three-point clip can create a cut along all three dimensions, depending on point placement.
Detail Brush
A detail brush is a type of brush that does not block the -VIS stage of the compiler. Summarily, any brush that does not provide structure/seal to a room, and merely is there to detail the room, should be made a detail brush [ctrl + M].
An object used to interact with the game, see GtkRadiant/Entities.
Entity Window
See GtkRadiant/The Entity Window.


A grid is a framework with vertical and horizontal lines in unison used to structure content. The grid, in GtkRadiant, is to the left, where you build your world.


A light is an entity that creates light and adds color to surfaces of brushes around it. Proper lighting can make any map look appealing.
A model is a pre-made piece of geometry which can be put into a map. The models available differ from game to game.
Npc is an abbreviation of non-player character (sometimes "non-playable character" or "non-player class"). It's a character in a computer game whose actions are not controlled by a human player.
The center point of the map, i.e. 0,0,0.
Patch Mesh
A sub-type of brush used to simulate curves in the Quake 3 engine. It is generated by a matrix of vertexes which can be moved independently of each other to form the curved shape. GtkRadiant has three standard types (Bevel, Endcap, and Cylinder) that will generate most needed curves, as well as the ability to create 'simple patch meshes' that allow for a free-form shaping. Patch Meshes are only visible from one side, and cannot be used reliably for fog, water, or any other spatial type of shader effect.
A prefab are a group of brushes which can be imported to your map. The difference between a prefab and a model are that prefabs sill consist of individual brushes whereas models are made out of already compiled polygons.
Q3Map2 The original tool created by Id to compile maps for the 'id tech 3' engine.
Q3Map2 Vastly improved Q3Map by ydnar.
A script is a set of written instructions used by the Quake 3 Engine to produce certain specific effects. There are two primary types - Shaders and Icarus Scripts. Typically, usage of the word script in forums or other media is a reference to the later, while the former is commonly referred to as a shader. Icarus Scripts are used to create effects in-game that can do anything from move a brush or set of brushes from point A to point B all the way to full Cinematics in SP games.
A script which defines the properties of the surface it is applied to. In fact, all textures which don't have a shader associated to them automatically get a default shader. Shaders are used to make lights glow, make floors be reflective, or make things non-solid or even water. Actually any special property a surface has is set by its shader. There are also many default shaders that come with the game such as caulk. In GtkRadiant all shaders have a white border around them when browsed in the textures browser.

A technique to make a more plastic sky.

An image or graphic which can be applied to a surface. See also shader.
The points between which the faces of the brush are drawn, usually the corners of a brush.
The gray area outside of the map itself, where nothing is. If there's a way to get to this area from any entity in the map, the map is leaked.
The entity that contains all the regular brushes in your map, so every brush you create will be added to the worldspawn entity.
A common mapping error relating to texture placement and brush alignment. It is cause when the faces of two brushes either completely or partially occupy the same plane, and are textured with either two different textures or the same texture with different settings. Visually in game, it is characterized by that plane showing both textures at the same time on that face, resulting is what looks like the textures 'fighting' to be shown.