{compiling} is about the process you must go through to convert your TeX from .tex source files into your output document format, be it pdf, dvi, or something completely different.
LaTeX is a compiled markup language, and as such there is a compilation process that needs to be followed to correctly produce output. This can be a long and complicated sequence of steps, with multiple passes being required to successfully build references and tables of contents amongst other things, as well as ensuring that externally generated files are up to date.
