A hyphen (-) is a punctuation mark used to join words (e.g. in "thirty-year-old piano") as compound modifiers, and sometimes to separate syllables of a single word (e.g. "re-educate") to either avoid ambiguity or separate two parts of a single word across a line break. Conventions do vary by style guide.

The hyphen should not be confused the minus sign (−); with an en-dash (–), or an em-dash (—); or with the horizontal bar (―), which can vary in length.