NORECOVERY: Tells SQL Server that you are not finished restoring the database and that subsequent restore files will occur. While the database is in this state, the database is not yet available, so no connections are allowed.
RECOVERY: Tells SQL Server that you are finished restoring the database, and it is ready to be used. This is the default option, and it is by far the one that is used most often.
STANDBY: Tells SQL Server that the current database is not yet ready to be fully recovered and that subsequent log files can be applied to the restore. You can use this option so that connections are available to the restore database if necessary. However, future transaction logs can only be applied to the database if no current connections exist.