Watermark describes an object of a predefined format which provides a point of reference for two systems/datasets attempting to establish delta/incremental synchronization; any object in the queried data source which was created, modified/changed, and/or deleted after the watermark value was established will be qualified as "above watermark" and could/should be returned to a delta-querying partner
Methodology
Watermark term is often used in Directory Synchronization software development projects. For example, products such as Microsoft Exchange Server, Active Directory, Active Directory Application Mode (ADAM), and Microsoft Identity Integration Server 2003/ Microsoft Identity Lifecycle Manager Server 2007, as well as Cisco Unified Communications Manager or Sun Microsystems IPlanet and other LDAP-based directory products are using DirSync and consequently will consume "watermark" object to provide efficient synchronization between directories. Watermark object sometimes can be referred as "cookie". DirSync control implementation can differ from product to product, however concept of watermark will allow any product to read changes in the directory incrementally.