Navigation refers to the links and menus on a website that allow users to move between different pages and sections. Effective navigation should be easy to use, learnable, and indicate the user's current location. When designing a navigation menu, it is important to start with information architecture and use simple, intuitive labeling. Navigation menus can be vertical lists or horizontal bars, and different link states like visited, hovered, and active can be customized with CSS. The document provides examples of code for different types of navigation menus and links.