Use this tag for questions about the Enterprise Geodatabase (ArcSDE in earlier versions) component of ArcGIS for Server.

ArcSDE is a component of ArcGIS for Server which enables ArcGIS client products and ArcObjects applications to access spatial data stored a Relational Database Management Systems (RDBMS). It presents that data as an Enterprise Geodatabase by either leveraging the underlying datastore's functionality (e.g., spatial indexes, xml fields, etc), or provides a default implementation if specific functionality is missing and thus cannot be delegated.