This tag is for questions about `gmake`, the GNU version of the `make` utility to maintain and update programs.
GNU Make is the GNU implementation of the Make utility. It is probably the most common version in use today.
GNU Make supports extensions to the Make language beyond the POSIX standard, therefore GNU Make solutions may not work under other versions, so the gnu-make tag is appropriate for questions from those using GNU Make, or pertaining to makefiles written for it.
Documentation
The latest GNU Make manual can be found in several formats here.