A product backlog is a dynamic and prioritized list of all the features, enhancements, and fixes that need to be implemented in a product. It serves as a roadmap for the development team, providing a clear understanding of the work that needs to be done and the order in which it should be completed. The product backlog is constantly updated and refined, with new items added and existing ones re-prioritized based on feedback, market trends, and business goals. It is a crucial tool in agile project management, allowing for flexibility and adaptability in delivering a high-quality product that meets the needs and expectations of the customers.