http://esther.mathematik.uni-osnabrueck.de/tex/tex/online-help/ltx-165.html (Einblicke ins Internet, 10/1995)A large document requires a lot of input. Rather than putting the whole input in a single large file, it's more efficient to split it into several smaller ones. Regardless of how many separate files you use, there is one that is the root file; it is the one whose name you type when you run LaTeX.