Well, there's the dictionary definition and then there's what we use in practice. I'll give practical advice, but know that there's more to this if you want to be pedantic.
Most people will refer to olddominionwildlife.com as your domain. Let's say you want another blog, you could host it at blog2.olddominionwildlife.com. If you wanted a forum you could host it at forum.olddominionwildlife.com.
As the domain owner, you have control over all subdomains and can create them at will.
Luckily, we here at Dreamhost can host as many domains and subdomains as we want on our accounts for the same price. You have to pay for extra domain registrations, but you can create subdomains for free.
If you're going to do all the hosting under the same user, the panel will default the space to /home/yourusername/yourdomainname.tld or /home/yourusername/subdomain.yourdomainname.tld. So in other words, you get a separate web directory under your user's home directory for each domain or subdomain you host. This is different from cpanel, if you're familiar with that.
Note that this can be slightly different if you choose to create a new user for that domain or subdomain.
Just that setting up a subdomain is a little easier in that you don't have to register a subdomain, you just add hosting for that subdomain in the panel at "Domains>Manage Domains".
extra domains and the new maximum $50 off with codes [color=#CC0000]1DOM50, 2DOM50 and 3DOM50[/color]. More Dreamhost coupons