Skip
Skip is a tool texture that tells the compiler (VBSP) to skip processing the brush face which is textured with it. It still exists inside the map although the engine (usually) ignores it at run-time.
Bug:In 
Counter-Strike: Source, skip brushes act as clip brushes for the bomb.
Tip:This can be exploited by a mapper to prevent the bomb from falling into a pit if planted too close to the edge.The Skip texture is used especially for Hint brushes. It is applied to the surfaces on brushes with the Hint texture that should not be used to break up visleaves (or leaves in short). Usually, a brush used for hinting has the Hint texture on one or two surfaces and the Skip texture on the rest. The Skip texture does nothing more than make the tools skip the brushsides they are applied to as a result of using the %compileskip VMT parameter.
The Skip texture can also be used to help preserve exact grid positions of other objects. Enveloping a group of precisely placed objects, inside a normal brush on par with a larger grid size, and then selecting these components together with the brush, will preserve the exact grid positions of the components when the group is moved according to the gridsize of the enveloping brush. As this brush is merely a tool for the design phase, covering the enveloping brush with the Skip texture will prevent this brush from being processed into the map. For detailed instructions, see the prefab article.
Warning:Never texture the faces of a brush with the Skip texture combined with non-tool textures. Texturing a brush entity with this texture will remove components of it from the map, which not only may result in compile errors like "bmodel 36 has no head node" but may also crash the game engine on load.
Texturing a world brush with this is fine as long as the only other textures on the brush are also tool textures. Using anything but tool textures causes bugs in-game.
Never use normal textures together with Skip on one brush. Instead, either replace Skip with Nodraw or use a Displacement.
Compiled version of the left picture. The game removed all faces of the brush, even though one is not a tool texture.
