The ability to dash properly is a useful skill, when working with running text for instance. Still, I often see otherwise dashing material that’s been dashed by being dashed off with a wrong dash. It’s a dashed shame.
Em Rule (n.): British. A dash of one em length that is used to create a strong sense of digression, associated thought, or an aside to the theme of a sentence.
Hyphen (n.): the sign (-) used to join words to indicate that they have a combined meaning or that they are grammatically linked, or to indicate word division at the end of a line.