As a quick share, I have a routine of writing down the details of tasks that are accomplished, either for clients, or on my own projects.
You are already familiar with how subdomains work, but the terminology may be new. Technically speaking, subdomains are part of the Domain Name System that is used to identify resources on the internet. For example, let's use Tumblr.com. If we add another name to the front, like this.. promediapublishing.tumblr.com, we have created a subdomain off the main domain. Very commonly you may see www.yahoo.com. The www part is actually a subdomain that allows website administrators the ability to direct traffic to different servers on a network.