The significance of a user persona in product development lies in its role in guiding design and decision-making. By creating detailed profiles of target users, including their needs, behaviors, and pain points, development teams can ensure that products align with user expectations. User personas facilitate empathy in the design process and help prioritize features that provide the most value. They also aid in effective marketing strategies by clarifying the audience, ensuring that communication resonates with real user experiences and enhancing overall product-market fit.