The solution slide is the pitch-deck slide showing what the startup built to solve the problem, plus the insight that makes the solution work. Typically the third or fourth slide of a pitch deck, it is designed to clearly communicate the product, why it's different from alternatives, and the insight or technological capability that makes the solution work now. It is the slide most founders over-design with product screenshots and under-communicate with story, missing that investors care about the insight far more than the interface.
The structure of an effective solution slide: one-sentence solution description (what the product is, in plain words a non-technical investor can repeat), the key insight or capability (the "aha" ...