User Account: A username and password in the SAM database of a workstation, server, or domain controller. A user account can be either local or global.
Group Account: An account that contains one or more user accounts whose purpose is to simplify sharing of and access to group-based resources. A group account can be either local or global.
Computer Account: An account consisting of a computer name, followed by a dollar sign. The account is a member of the Domain Users global group in the SAM database of a domain controller. NT creates a computer account when a workstation, server, or Backup Domain Controller (BDC) joins a domain. Computer accounts provide secure communication between a workstation or server and a domain controller, and between domain controllers in the same domain.
Trust Account: An account consisting of the trusted domain name preceeded by G$$. NT creates this account between a domain controller in a trusted domain and a domain controller in a trusting domain when it establishes the trust relationship. Trust relationships ensure secure, interdomain communication and are essential for passthrough authentication.