The terms "menu", "navigation" and "navigation bar" play an important role in web design. Here is a simple explanation of each term:

1. menu: A menu is a list or collection of options displayed on a website. It helps visitors to find and select different pages or functions on the website. A menu can take the form of text links, buttons or icons. It serves as a navigation tool to make it easier for users to browse a website.

Example: Imagine you are visiting a restaurant website. The menu on this website shows different categories of dishes such as starters, main courses, desserts etc.. When you click on one of these categories, a list of the corresponding dishes opens for you to choose from.

2. navigation: Navigation refers to the process of moving or navigating through a website. It involves the use of menus, links or other elements to move from one page to another or to reach specific content on a website. Navigation is crucial to providing users with a good user experience and ensuring that they can easily find what they are looking for.

Example: Suppose you are on an e-commerce website that sells clothing. To find the product you are looking for, you can use the navigation by clicking on the different categories, such as women's clothing, men's clothing, shoes, etc. Within each category there are further sub-categories that allow you to find the exact product you are looking for.

3. navigation bar: A navigation bar is a horizontal or vertical bar element on a website that is usually placed at the top or side. It contains links or buttons to the most important pages or areas of the website. The navigation bar usually remains visible on every page of the website to allow users to navigate easily, regardless of which page they are on.

Example: Consider a blog website. The navigation bar could contain links to the main pages such as "Home", "About us", "Contact" and "Archive". No matter which page you are on, you can easily get to other important pages on the website by clicking on the corresponding links in the navigation bar.

To summarise, menus, navigation and navigation bars in web design are used to make it easier for visitors to find and reach certain pages, content or functions on a website. They are important tools for improving the user-friendliness and efficiency of a website.