Hyphens, em-dashes and en-dashes

We all know what a hyphen is; it cohabits with an underscore, sharing the same key on the standard english language keyboard.

But what about its less identifiable cousins, the en-dash and thee m-dash?

They are so called because of the length of a dash, being the same as the width of the respective letters n and m.

underscore _
hyphen -
en dash –
em dash —

Typically the american preference is for an em dash without a space, while the UK traditionally uses a spaced en dash.

An example of this—for example - would be the preceding.

A hyphen, on the other hand, serves to join together two words, to create a compound of double-barrelled word.