When we browse through the internet and sometime considering to purchase domain/ web hosting, we often found in the list of features that is offered by the web hosting company terms like domain, subdomain, add-on domain, parked domain. What does this all means?
Before we proceed, if you would like to gain an understanding about what is domain name, please refer to our previous article here 
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Subdomain
Subdomain is a prefix added to your primary domain. For example, if you own a domain name e.g., mybrand.com then shop.mybrand.com, blog.mybrand.com are subdomain of mybrand.com.
They behave like domain name and normally was created to separate a different section of the website. But the usage of subdomain can be more than just to point a different section of website. Subdomain can be hosted in a different server, or mapped to a different services related to the domain. For example, rather than pointing the visitor to your website to your youtube channel link (e.g. www.youtube.com/yourchannelname, you can use youtube.mybrand.com to redirect the users to your youtube channel. Similarly you may have a facebook pages relating to your business with an address of www.facebook.com/yourpages address, you can use fb.mybrand.com to be mapped to your facebook page.
Recently, subdomain mapping are also used to map to your official whatsapp account, telegram account, etc. With many creative use of subdomain, you can built consistent branding for all your related services and communication channel. Your customer do not need to remember, the difference URL/ link to your different social medial channel. The just need to remember your domain, e.g. mybrand.com and if they would like to sent a whatsapp message, just type whatsapp.mybrand.com (as an example) then their phone will automatically redirect them to whatsapp messenger to your account.
Add-on Domain
Add-on Domain is fully functional domain that is hosted in the same web hosting account as your main domain. Assuming you have a web hosting account for the domain mybrand.com. Depending on your web hosting plan, you can add another domain, say mybrand.net to also been hosted within your account and share the resources (i.e. storage space, CPU and RAM) of your account. If you are using cPanel, the add-on domain will normally will be separated by a different sub-folders in your main account. It will also have a separate email, etc. Because of the separation through a different sub-folders, there will not be an issue of visitor to mybrand.com can see what is in mybrand.net and vice versa. Visitor to mybrand.com will be forwarded to your main directory/ folders. Visitor to mybrand.net will be forwarded to your sub-directory/ folders.
Why people might opt to have add-on domain? Ease of administration. Since the two domains, e.g. mybrand.com and mybrand.net is owned by the same company/ person, it make sense to have one web hosting account rather than having to login to a different server or account for your multiple web sites/ brands.
Parked Domain
Unlike add-on domain which will be have a different folder in your web hosting account, hence technically can have a different websites and data, parked domain, is a fully functional domain that you parked on your web hosting account to be mapped to your existing folder. Example will be, let say you have two domain name e.g., mybrand.com and mybrand.net. But instead of having separate web site, you wanted both domain to open the same website. Sometime people refer this as domain alias.
