From Quake Wiki
This page is about stuff like customizing your HUD, crosshair, using replacement textures, etc, in engines that support it.
[[configuration file]] This article will show you what variables that a user can easily modify or add so that certain keyboard or mouse commands can be tied to them. This article is not intended to be a detailed explanation of how these variables work.
[[Configuration details]] This is where specific configuration command issues are addressed and the possible implications of using them are discussed.