A service that
1. provides a safe environment for your website to live — in other words: disk space to store the website files
2. makes the website accessible to others via the internet
One of the first principles we discussed as we were building our hosting capabilities back in the day was the idea of being in a position of strength. Problems can and will happen, but we want to be in a position where, as much as possible, we are shielded from inevitable failures. That means identifying points of weakness and having contingency plans, not blindly taking others' assurances, and not relying totally on things we have no control over.
It's why we're so careful where our servers and our data are located. It's why we try to host domain registrations and DNS for clients ourselves whenever possible. And it's why we spend time learning, testing, and adapting to change.
And it's part of why it really does matter who you trust to manage your digital presence.