Put simply, a domain is what you would usually refer to as your website’s URL.
An example of a domain: wphosting.com.au (or http://wphosting.com.au)
– Notice the domain name and .com.au extension?
An example of a sub-domain: hello.wphosting.com.au (or http://hello.wphosting.com.au)
– Notice the sub-domain name “hello” followed by a dot “.”?
An example of a directory: wphosting.com.au/hello (or http://wphosting.com.au/hello)
– Notice the forward-slash “/” then the directory name “hello”?