When an output line is nearly full,
it is uncommon for the next word collected from the input
to exactly fill it—often,
there is room left over for only part of the next word.
Hyphenation
is the
process of splitting a word so that it appears partially on one line,
followed by a hyphen to indicate to the reader
that the word has been broken,
and that its remainder lies on the next.
Hyphenation break points can be manually specified;
GNU
troff also uses a hyphenation algorithm
and language-specific pattern files
(based on
TeX’s)
to decide which words can be hyphenated and where.
Hyphenation does not always occur even when the hyphenation rules for a word allow it; it can be disabled, and when not disabled there are several parameters that can prevent it in certain circumstances. See Manipulating Hyphenation.