These are slides in your VCDX deck that include a logical diagram of an alternative decision for a specific item in the design.
What that means is if you went for Fiber Channel storage and Classic Ethernet on a blade form factor an alternative slide might include a converged solution that still would have fulfilled the business requirements but was not chosen for any number of reasons you need to know and explain if asked on the matter.
Lets use another demo slide example: Blade Form Factor vs. Rack Server Form Factor
Text can include Pros and Cons, how this design was not chosen or risks involved with this layout. Just based on the comfort level of remembering the justifications in detail.
Please be sure you are ready for follow up question regarding a specific setup. So if you bring up FCoE, you need to have Minimally Qualified VCDX subject matter knowledge on the matter if asked (not that any body knows what that exactly is, except for the panellist). Example questions might be: Explain how FCoE is different from native Fiber Channel? What is required to enable FCoE? Etc.