Why do some privileges appear greyed-out?

If a user privilege is greyed-out, this means the privilege belongs to a user account role. Bold-colored checkboxes indicate a privilege is assigned individually to the user. It's possible for users to have a combination of privileges—both individual privileges and privileges inherited from user account roles.

Hint: If you manually select a greyed-out privilege and make it bold, that privilege will remain with the user even if the underlying user account role is removed from their user account.