[nottorp]

I thought there's a minimum length for domains. How was Twitter even allowed to get x.com?

[quesera]

There used to be a minimum length for .com, .net, and .org. It was enforced by the registry to avoid confusion or special-case privileging.

When domain names became big business, those rules were changed.

Another old rule is that the domain name could not start with a digit.

[h2odragon]

Elon bought "x.com" from the folks who registered it very early on.

He's been looking for an excuse to use it ever since paypal.