An Independent Action Group (IAG) contains a set of actions that are independent. That is, each action is not dependent on completing a previous action before it is available.
The entire IAG, however, acts as a dependent set. In other words, the IAG is not available until the previous action is completed. Likewise, the action immediately following the IAG is not available until every action of the IAG is completed.
To state this another way, the Independent Action Group is a single, dependent set of actions within the list of dependent project actions.
As a project evolves, it may be necessary to move the IAG to a different position.
Moving an Independent Action Group
When one or more Independent Action Groups are present in a list of project actions, the Sort Mode icon will appear in the header.
Normal Sort Mode

In Normal Sort Mode, drag an action and:
Drop it anyplace inside the group to move it to a new position.
Drop it outside of the group to remove it from the group.
Group Sort Mode

In Group Sort Mode, drag any group action and drop it outside of the group to move the IAG to a new position.