A warm standby application is a pair of Adaptive Server databases, one of which is a backup copy of the other.
Client applications update the active database; Replication Server maintains the standby database as a copy of the active database. If the active database fails, or if you need to perform maintenance on the active database or on the data server, a switch to the standby database allows client applications to resume work with little interruption. Warm standby applications topics describe how to set up and configure a warm standby application between two Adaptive Server databases—the active database and the standby database.
See the Replication Server Administration Guide Volume 2 > Manage Warm Standby Applications for detailed information about warm standby applications, how it works in Replication Server, and other related topics.
Most of the times in Replication Server, databases are defined as "primary" and "replicate." However, in discussing warm standby applications databases are also defined as "active" and "standby."