Compiling a map is the process of turning a
map file used by an editor (usually a .map or .rmf file) into a file that can be run by the game itself (a .bsp file).
The compilation process runs through four programs known as compile tools. These are, in order,
CSG,
BSP,
VIS and
RAD. Each are responsible for a different tasks. Compile tools are typically distributed and run as a full set. Editors and batch compilers usually offer a range of advanced options for each tool.
In order to get the best results (and run into the fewest issues) with mapping, it is always a good idea to make sure you are using the best compile tools available. For
GoldSrc, the
VHLT tools are currently the ideal tools.