autoconf expands the m4 macros in `configure.in' , perhaps using macro definitions from ` aclocal .m4' , to generate the configure script.
autoconf
m4
configure
user input files optional input processes output files ================ ============== ========= ============ aclocal.m4 - - - - - -. V .--------, configure.in ----------------------->autoconf------> configure `--------'