A Hostname must assign a unique name to your VPS. Every computer has a name (called hostname). Often, this will actually be a real DNS name, but technically, it can be anything.
For example, you own AccuWeb Hosting, so it is always common to pick a hostname using it; for example, you may choose vps.accuwebhosting.com as your hostname.
If you do not own a domain name or just do not care, you can technically enter anything that's a valid hostname. For example, you could enter"vps.yourname.com". If you ever desire, the host nameservers can be easily changed after the installation.