Here is some typical terminology when using Design Options. This was originally written by a colleague of mine a few years ago...so I thought I'd recycle it...
Thanks Bruce ;-)
The main model encompasses all the features of the design that are not optional.
Design Option Set
A design option set is an agreed-upon collection of alternatives that addresses a particular design issue.
A design option is one possible solution to the design problem, so each design option set will normally have more that one design option. Each design option is specific to the issue addresses in the set. You can have only one primary option per set.
You can dedicate a view to a specific design option for each design option set using the Design Options tab on the Visibility/Graphics Overrides dialog box. When this view is active or added to a sheet, the option set you have dedicated is always shown along with the main model.
Any option that is an alternative to the primary option in the same option set. Elements in the secondary option can reference elements in the main model, however elements in the main model cannot reference elements in the secondary option.
When design options are enabled, you can control the visibility of design options in plan views, elevation views, 3D vies and drafting views through the Design Options tab of the Visibility/Graphics Overrides dialog box. By default, the visibility of a design option is set to automatic. This means that the view displays the main model and the primary option if there are no options being edited. If you are editing an option, the view displays the main model and the option you are editing. You can dedicate the view to use a specific option within an option set by choosing the option name.
For further information refer to some of my other blogs on Design Options:
How too guide: http://bim4scottc.blogspot.com/2011/08/design-options-how-too-guide.html
Design Options Graphics: http://bim4scottc.blogspot.com/2011/08/design-options-graphics.html