A demonstration is showing how your deliverable actually works or let the audience try it themselves. Do not present your work or how your product works. End users don’t get that information neither. Just demonstrate it, accompanied with a very brief explanation. Explaining a feature in a presentation takes a lot of time, while demoing it takes no time at all. The proof of the pudding is in the eating.
Imagine you came up with the invention to tie shoe laces. What would be easier and shorter for the audience? Demonstrating how to tie shoe laces or make a presentation explaining it? You can demonstrate how to tie shoe laces in 5 seconds.
This is also why music producers always play an edit after changing some settings in a mix. That is the real evidence. Adjust, play, listen, adjust, play, listen.
If you can’t demo a real working sample, then a good alternative could be a quick video. Remember, as real as possible. In order to experience in a rich way and decide what to do next. If it is not real enough, you can not make a reliable judgement.