The 3-click rule is a user experience design principle that states a website or application should be designed in a way that allows a user to find the desired information or complete a task within three clicks or less. This rule aims to improve the usability and efficiency of a website by minimizing the number of steps a user needs to take to achieve their goal. By following the 3-click rule, designers can ensure that their website or application is intuitive and user-friendly, ultimately enhancing the overall user experience.