User personas are significant in product design as they represent the needs, behaviors, and goals of target users. By creating detailed profiles based on user research, designers can better empathize with users and understand their pain points. This understanding helps inform design decisions, ensuring that products are user-centered and meet actual needs. User personas also guide features and functionality, prioritize development efforts, and enhance marketing strategies. Ultimately, their use fosters innovation and enhances user experience, leading to greater customer satisfaction and loyalty.