An NDA is a way of allowing you to tell some things, but not the whole story. It is analogous to if you told someone a family recipe for cookies. “A little flour, sugar, vanilla extract, a special blend, and baking”. You tell them some things (that are public knowledge) and something that says you do something different. However, you do not tell them what that different something is, you leave it a mystery. An NDA outlines what is enough info to get people interested in the company’s product without risking the company IP. As an employer, I would use an NDA to describe what a presentation about the product would entail. Just enough to capture attention. Where would you draw the line between interesting information and too risky?