There are three domain types: Parked Domains (Alias), Sub Domains (subdomain), and Addon Domains.
1. Parked domain: A parked domain is a domain name (eg; example.com) that points to the front page of the main domain. You can not park a domain over a sub. domain or an add-on domain.
2. Subdomain (domain.webhostpro.com) is when you replace www. with any word you want. For example, a common sub. domain is news.google.com. As you can see there is no www. like most URLs instead there is a term used to explain what that locations offer.
3. Addon domains are the most popular of the three, this powerful tool allows you to add top-level domain names to any folder in your domain. For example, if you have a second domain called your-main-domain2.com, you can have that domain point to your-main-domain.com/addonfolder or any other folder you want. It is almost like receiving more web hosting accounts for free.
All three of these tool options are available in website hosting, website builder, and reseller hosting packages.