Making Consistent and Inconsistent Backups with RMAN

CONSISTENT

A consistent backup of the database is one taken when the database is in a consistent state, that is, one, after the database has been added to normal down (with SHUTDOWN NORMAL, SHUTDOWN IMMEDIATE or SHUTDOWN TRANSACTIONAL).
At this point, all changes in the redo log have been applied to the data files. If the database and mount a backup at this point, you can restore the database from this backup at a later date and open it without performing media recovery.

INCONSISTENT

Any backup taken when the database was NOT shut down normally an inconsistent backup.
If a database is restored from an inconsistent backup, Oracle must recovery media, run before the database can be opened, applying any pending changes from the redo logs.

Click Here for RMAN Scenarios