alphanumeric characters in username

[scootergrisen]

There is a string that says:
"Invalid username. All usernames must be between 1-20 characters, and only include "-" and alphanumeric characters"

But in my language we dont say alphanumeric so its not so clear for me exactly what i can use.
Does it include "-" 0-9 a-z A-Z and nothing else ?