Key Takeaways:

Menu areas are the regions inside a WordPress site into which WordPress navigation menus can be inserted. As a presentational element of a site, menu areas should be registered in the theme.
WordPress menu areas are often called simply "navigation menus." However, this risks confusing menu areas with the actual menus themselves—which the user creates and customizes in the WordPress admin area. The best term is "menu areas": zones into which user-created navigation menus can be added.
The key functions to register and display navigation menu areas are register_nav_menu() and wp_nav_menu(), respectively.

Navigation menu areas—the areas in the theme where user-defined nav menus may display—are a key component of theme development. In this chapter, we'll cover registering and displaying nav menu areas.

The WordPress nav menu area API has quite a lot in common with the widget area...