\-
(discretionary hyphen)
The \-
command tells LaTeX that it may hyphenate the word at
that point. LaTeX is very good at hyphenating, and it will usually
find most of the correct hyphenation points, and almost never use an
incorrect one. The \-
command is used for the exceptional
cases.
When you insert \-
commands in a word, the word will only be
hyphenated at those points and not at any of the hyphenation points
that LaTeX might otherwise have chosen.