On networks and multiuser operating systems, the set of rules that defines whether a new user is permitted access to the system and whether an existing user is granted additional rights or expanded access to other system resources. Account policy also specifies the minimum length of passwords, the frequency with which passwords must be changed, and whether users can recycle old passwords and use them again.(Ref: Dyson, Dictionary of Networking)
With Windows NT computers, controls the way passwords must be used by all user accounts of an individual computer. With Windows NT Advanced Servers, controls the way passwords must be used by all user accounts of a domain.
Controls the way passwords must be used by all user accounts of a domain, or of an individual computer. Specifics include minimum password length, how often a user must change his or her password, and how often users can reuse old passwords. Account policy can be set for all user accounts in a domain when administering a domain.