Design principles are a set of guidelines that shape the way a product team approaches design. They can include things like user-centered design, simplicity, and accessibility, and serve as a foundation for the team's design decisions. Design principles help teams to create products that are intuitive, user-friendly, and visually appealing, and can serve as a reference point when faced with design challenges. By adhering to design principles, product teams can create user experiences that are consistent, effective, and aligned with the company's values and goals.