It’s an obsession with literature and/or typography nerds specifically.

Option-shift-hyphen types an em-dash, option-hyphen an en-dash. Em dashes are used—like this—as something spiritually akin to a parenthetical. En-dashes are used within ranges: the Feb 14–17.

silly specific: the minus sign is a separate character. The dash equivalent is the en dash (–), versus the larger em (—) and smaller hyphen (-).

The en dash is also used in things like scores (3–2 Turkey), votes (the bill passed 58–42), or connecting words where the second part is longer than one word (the Australia–New Zealand alliance.) You can remember the latter as, "a hyphen isn't big and strong enough to hold on to more than one word.

If you're on a mac, pressing Option+- is the en dash and Option+Shift+- is the em dash.

Depends on your OS. Mac is the easiest, it's just ---, Linux depends on your distro, if it uses KDE, it's <right-win>--- —. Windows is a little awkward, I think you need <right win>+the code point.

In emacs, c-x 8 RET prompts you for unicode character names (or hex) so for rare use you can just spell it out. There's also C-x 8 _ m for em dash and C-x 8 _ n for en dash. (Hit c-x 8 c-h to get a full list of those bindings, like any normal secondary map - they're about as idiosyncratic as the XCompose bindings, but you might find some of them "stick" in your head better (I personally like "C-x 8 1 / 2" better than "Compose 1 2" even if it's a lot more typing...)

> How do you type an em-dash? Is it OS specific?

On Linux X11 at least, you can enable the Compose key and then press `<Compose>---` which results in — and `<Compose>--.` which gives you –

Keyboard layout specific. Macs with their default English layout use “option-shift-dash” which is really easy to remember (and relatively discoverable, as such things go) which is why using proper m-dashes (not just double-dashes) used to be a strong indicator a poster was using a Mac, before LLMs took the character over.

On iOS you type it by pressing dash and holding until alternative options come up, same way you type e.g. accented characters.

Macs have a native way to do dashes: option- hyphen for en-dash and option shift hyphen for em-dash. On Windows there are some application-specific ways that make sense, e.g. in Office, but outside that you’re on your own and have to use the “hold alt and type the character codes” method! Or charmap.