The TLD .org was originally for non-profits, to distinguish them from the for-profit companies found over at the .com TLD. In the beginning, you had to prove nonprofit status to get a .org domain.

That’s no longer required, but still there was a big fight a few years ago when the .org registrar was set to be sold to a private equity firm. It’s the TLD of choice for nonprofits, as an echo of that early restriction.