These are lines on which the first character is "#". These allow you to tell the compiler to include a separate text file at this point in the current file. You can "nest" these directives in up to five levels of files. The syntax is:
#include <filename>
where <filename> is either a full path plus a filename, or just a filename without a path. If no path is given, then the compiler assumes that the file is in the same directory as the top level input file. Examples:
#include c:\msword\interps\aspects.txt
#include extra.txt