Relationship between Account User Domain

Yes, one cPanel account can have multiple domains. There are two types of "additional" domains.

First, there are "Parked Domains" which are essentially additional domains that serve the same content but it just looks like it's from a different address. This can be useful if your account is for example.com but you also want example.net to point to your website.

Additionally, there are "Addon Domains." These are not the same as Parked Domains. Instead, they serve completely different content than any other domain on the account. Documents can be served from anywhere within the user's account (even outside public_html).