roff is the general name for a set of text formatting programs, known
under names like
groff, etc. A
system consists of an extensible text formatting language and
a set of programs for printing and converting to other text formats.
Unix-like operating systems distribute a
roff system as a core package.
The most common
roff system today is the free software implementation
groff implements the look-and-feel and
functional‐ ity of its ancestors, with many extensions. -- From the
man roff manual page, copyright Free Software Foundation, Inc. See the
man page for a longer history.