An em dash (—) is again, very different from a hyphen (-). Em dashes are used to replace punctuation (such as commas, parentheses, colons, and semicolons) or are used to show an interruption or represent missing words or parts of a word. Hyphens have many uses, but it does not replace punctuation like em dashes do. The key way to remember the difference between these two is not only the size difference, but also that em dashes do not appear within a word, but hyphens always do.