What does -L option mean?

The -L option in the Hydra command specifies a file that contains a list of usernames to be used during the login attempts. Each line in the specified file represents a different username that Hydra will try in combination with the passwords provided (using the -P option) against the target service.

For example, if usernames.txt contains:

user1
user2
admin

Hydra will attempt to log in using each of these usernames with the passwords from the passwords.txt file. If you have more questions or need further clarification, feel free to ask!