1  –  role-name

    The name of a role previously created with the CREATE ROLE
    statement. If the role name exists as an operating system
    group or rights identifier, then Oracle Rdb will automatically
    create the role when you issue the GRANT statement. A role that
    is created automatically always has the attribute IDENTIFIED
    EXTERNALLY.

2  –  TO

 Syntax options:

    TO username | TO role-name | TO PUBLIC

    Specifies the user name, role name, or the PUBLIC user to which
    you want to grant the role. The PUBLIC user is the user name
    associated with all anonymous users who access the database.

    If the user name or role name exists as an operating system user
    or rights identifier, then Oracle Rdb will automatically create
    the user name or role name when you issue the GRANT statement.
    A role or user that is created automatically is IDENTIFIED
    EXTERNALLY.