Macro definitions can be collected into macro files, roff
input files designed to produce no output themselves but instead ease
the preparation of other roff documents. There is no syntactical
difference between a macro file and any other roff document; only
its purpose distinguishes it. When a macro file is installed at a
standard location and suitable for use by a general audience, it is
often termed a macro package.29 Macro packages can be
loaded by supplying the -m option to GNU troff or a
groff front end. Alternatively, a document requiring a macro
package can load it with the mso (“macro source”) request.