Em dash

Em dash

The em dash, em rule, or mutton dash— is longer than an en dash. The character is called an em dash because it is one em wide, a length that varies depending on the font size. One em is the same length as the font's height (which is typically measured in points). So in 9-point type, an em dash is nine points wide, while in 24-point type the em dash is 24 points wide. By comparison, the en dash, with its 1 en width, is in most fonts either a half-em wide or the width of an upper-case "N".