It's basically asking "What is the one thing (or "main thing") you do differently than the other companies you'll be competing with?" It's a metaphor for how sandwich/burger shops will tout their "secret sauce" that makes their sandwiches/burgers the "best in town". It's like the formula for Coca-Cola, or KFC's "secret blend of seven herbs and spices", but in technological terms or business terms.
In those terms it might be a new algorithm you invented (like "the compression algorithm" from Season 1 of Silicon Valley) or something unique about your business model. It could even be a business relationship, like an exclusive deal with a supplier of some exotic material or component or something.