A dash is a little horizontal line that floats in the middle of a line of text (not at the bottom: that’s an underscore). It’s longer than a hyphen and is commonly used to indicate a range or a pause. Dashes are used to separate groups of words, not to separate parts of words like a hyphen does. There are three forms of dashes: em, en, and the double hyphen.
The most common types of dashes are the en dash (–) and the em dash (—).