The term Standby Database is used in the following situations:
Standalone Standby Database
A standby database is a copy of the active database, which you update regularly using the log backups of the active database.
More information: Database Administration, Standby Databases
Standby Databases in hot standby systems:
In a hot standby system, the content in one or more standby databases are regularly updated to match the content of a master database. If the master database fails, one of the standby databases becomes the new master database. Standby databases are always in the STANDBY operational state.
More information:
Database Administration, Hot Standby System
Database Studio, Setting Up Hot Standby Systems: Overview
Database Administration in CCMS, Properties
Database Manager CLI, Managing Hot Standby Systems