Its an authoritative DNS service, so it can host your domains.

Compare with a recursive resolver, like 8.8.8.8 or 1.1.1.1, which you can use to resolve domains.

What's nice about Bunny DNS is that they have authoritative nameservers ~everywhere, so resolving is quick everywhere.

But I think in practice this isn't that useful, since if a domain is moderately used, its DNS records will be cached ~everywhere in anycasted recursive resolvers.

You were looking at the website of Bunny, which is a company that offers primarily a CDN service, as well as other related things like compute hosting, object storage, DNS etc.

It's comparable to Cloudflare, if you're familiar with that, though Bunny is based in the EU instead of US.

This post is about their scriptable DNS service, which used to be paid and is now free.