By definition, a domain name is simply a human readable form of an IP address. In function it is the destination that you type into a web browser in order to visit a website, such a www.google.com. Metaphorically, it is very similar to how you would scroll to a contact in your cell phone rather than manually dialing the person by entering their full phone number; the phone number would be an IP address and the saved contact would be a domain name. Always buy a domain with a reputable domain registrar.
Bluehost does offer an automatic backup system along with daily scheduled backups, albeit these are only included for free with certain hosting plans. However, you can add a backup system to the packages that don’t already include it for just $3 a month, which is a small price to pay for keeping your files safe. That, or you can simply back up your files via FTP as mentioned earlier.