An offline backup is a copy of the database files. You can make offline backups by copying the database files when the database is not running.
An online backup is performed against a running database. Backing up a running database provides a snapshot of the database when the data is in a consistent state, even though other users are modifying the database.
A live backup is carried out by using the dbbackup utility with the -l option. A live backup provides a redundant copy of the transaction log for restarting your system on a secondary computer should the main database server computer become unusable.