In typography, a unit of measure equal to the width of the capital letter M in a particular font. The terms "em" and "en" are widely heard with regard to the dashes commonly found in typography, but which are not standard keyboard keys. An "em dash" (one em wide) is used to convey changes such as an abrupt break in thought, a digression or a change from one speaker to another. "En dashes" (width of letter N) are shorter and are used for ranges such as numbers and dates. Contrast with the hyphen, which is a regular text character used to separate telephone and account numbers.
Em and En Dashes in HTML
The mdash and ndash are the codes used to create em and en dashes on HTML pages, whereas the hyphen is a regular text character in HTML.
