Your domain is the name. Your DNS translates that name into addresses. Your hosting is where the site actually lives. They are frequently at three different companies, and nothing forces them to be together.
Why this matters when something breaks
If the site is unreachable, the cause could be any of the three. The most common wasted hour is someone checking their hosting when the domain has expired, because the registrar panel still showed the domain as active.
How to tell which is which
- Registrar — where you pay the annual renewal. Shown in any domain lookup.
- DNS — wherever your nameservers point. Often the registrar, often Cloudflare, sometimes the host.
- Hosting — where the files are. Identifiable from the IP address the domain resolves to.
Why they drift apart
A site gets rebuilt and moves host. DNS gets moved to Cloudflare for speed. The domain stays where it was registered a decade ago. Nobody documents any of it, and three years later nobody can say where anything lives.
This is the short version. The full guide covers it properly: read more.
On how changes actually reach people: the TTLs and propagation field guide.