In addition to various unuseful abbreviations, ms is most importantly the name of a package of text formatting macros for troff and nroff (and therefore for groff, too). ms "provides a formatting facility for various styles of articles, theses, and books". Indeed, several books have probably been produced using this macro package (in conjunction with tbl, pic, grap, refer and eqn, most likely).

Compare with me, which is intended to provide facilities for "technical papers".