This topic is relevant only for backup and restore of SQL Server databases that are using the full or bulk-logged recovery models.
A tail-log backup captures any log records that have not yet been backed up (the tail of the log) to prevent work loss and to keep the log chain intact. Before you can recover a SQL Server database to its latest point in time, you must back up the tail of its transaction log. The tail-log backup will be the last backup of interest in the recovery plan for the database.
NOTE: Not all restore scenarios require a tail-log backup. You do not need a tail-log backup if the recovery point is contained in an earlier log backup. Also, a tail-log backup is unnecessary if you are moving or replacing (overwriting) a database and do not need to restore it to a point of time after its most recent backup.