A Windows domain is a network structure used in Microsoft Windows environments that allows for centralized management of computers and user accounts. In a domain, multiple computers can be connected and managed under a single set of rules and policies, making it easier for administrators to control access and security settings. Within a Windows domain, user accounts are stored in a domain controller, which authenticates users and grants them access to resources like files and printers. This setup enhances security and simplifies the management of user permissions across the network, ensuring that users have the appropriate access to the resources they need.