Administrative Templates are a feature of Group Policy, a Microsoft technology for centralised management of machines and users in an Active Directory environment.
Administrative Templates facilitate the management of registry-based policy. An ADM file is used to describe both the user interface presented to the Group Policy administrator and the registry keys that should be updated on the target machines. An ADM file is a text file with a specific syntax which describes both the interface and the registry values which will be changed if the policy is enabled or disabled.
ADM files are consumed by the Group Policy Object Editor (GPEdit). Windows XP Service Pack 2 shipped with five ADM files (system.adm, inetres.adm, wmplayer.adm, conf.adm and wuau.adm). These are merged into a unified "namespace" in GPEdit and presented to the administrator under the Administrative Templates node (for both machine and user policy).