What is the term 'Access Group' in RTC and how is it related to streams/components?

In RTC 6.0.1 the ability to read protect SCM artifacts for a select group of users, project area members, or team area members, by means of an access group was added. Streams, repository workspaces, components, files, or folders can all have their read access determined by an access group.

This new feature is briefly described in the 6.0.1 New and Noteworthy here:
https://jazz.net/downloads/rational-team-concert/releases/6.0.1?p=news#access-groups

There is a jazz.net article called "Controlling access to source control in Rational Team Control" which explains this new feature in a little more detail here:
https://jazz.net/library/article/215#access_groups

There is also a YouTube video showing how to use Access Groups for SCM Artifacts here:
https://www.youtube.com/watch?v=TJM56oVQNMc

Please see

https://rsjazz.wordpress.com/2016/01/27/manage-access-control-permissions-for-work-items-and-versionables/ and
https://rsjazz.wordpress.com/2016/02/03/setting-access-control-permissions-for-scm-versionables/ .

Ignore the talk about the API but learn the options explained.

Access groups are basically groups of project areas, team areas and users administrators can create and maintain. These access groups can be used to restrict read access to certain objects.