Explanation

Box 1: SINGLE_USER
The specified database must be in single-user mode to use one of the following repair options.
Box 2: REPAIR_ALLOW_DATA_LOSS
REPAIR_ALLOW_DATA_LOSS tries to repair all reported errors. These repairs can cause some data loss.
Note: The REPAIR_ALLOW_DATA_LOSS option is a supported feature but it may not always be the best option for bringing a database to a physically consistent state. If successful, the REPAIR_ALLOW_DATA_LOSS option may result in some data loss. In fact, it may result in more data lost than if a user were to restore the database from the last known good backup.
Reference:
https://docs.microsoft.com/en-us/sql/t-sql/database-console-commands/dbcc-checkdb-transact-sql