Only available for Windows Server editions
Utilizing a server to store users and passwords.
A windows domain server stores all users. All local computers can be logged onto with the users stored in the domain server.
It aims to secure data.
Joining A Domain
Settings > About PC > Rename this PC (Advanced) > Computer Name > Change > Input the domain you want to join
Domain Users
Logging into a domain will require the username be in the form of:
<Domainname>\<Username>