A Blog Domain is a unique name for a blog that you create in WordPress. It is the name that you use when you sign up for a WordPress account, and it is also the name that appears in the address bar of your web browser when you visit your blog.
When you create a blog in WordPress, you first choose a name for your blog domain. This name can be anything you want, but it must be unique within the WordPress network.
You can then enter your blog domain into the address bar of your web browser and hit ENTER. .
WordPress will then automatically create a blogspot.com account for you with that domain name as the login name and the default password. You can now start blogging!
If you ever need to change your blog domain name or login name, all you have to do is contact WordPress support and they will help you out.