JAAS, authorization and role groups

[jimi_usenet]

I'm not sure if this is the right newsgroup for this question, but I
think it is about JAAS (Java Authentication Authorization Service).

In the configuration of the security policy I can provide something
called a rolesQuery. And the explaination is:
"The prepared statement query equivalent to: select Role, RoleGroup
from Roles where PrincipalID=?."

This is from the manual for JBoss, but I guess the term role group is a
general term used in the field of authorization. But what is a role
group, exactly? And what can be achieved by using them?

http://www.huihoo.com/jboss/online_manual/4.0.1/ch8.chapter.html (go
down to section 8.4.6.4)

Regards
/Jimi