In Active Directory Lightweight Directory Services (AD LDS), a "service instance" (or, simply, "instance") refers to a single running copy of AD LDS. Multiple copies of AD LDS can run simultaneously on the same computer. (This is not true for Active Directory Domain Services (AD DS.) Each instance of AD LDS has a separate directory data store, a unique service name, and a unique service description that is assigned during installation. An instance can be part of a configuration set that provides replication of instance data to instances that run on separate servers.