The phrase "top navigation" refers to the menu or bar that appears at the top of a website or app. It helps users easily find and access different sections or pages of the website or app. Full definition
That means that, when you click on links to move around within the application, the left and top navigation bars stay in place. (lawsitesblog.com)
Then, one tip: when I am on my tablet and turn it portrait, your logo and top navigation disappear. (michelle-tyler.com)
A better user experience With a brand new top navigation menu on every page, visitors can now seamlessly transition between the site's most relevant pages to easily find the content they are looking for. (lawyermarketing.com)