A tab page holds one or more windows. Questions about how to use and customize the behavior of Vim tabs.

From :h tab-page-intro:

You can easily switch between tab pages, so that you have several collections of windows to work on different things.

Usually you will see a list of labels at the top of the Vim window, one for each tab page. With the mouse you can click on the label to jump to that tab page. There are other ways to move between tab pages, see below.

Most commands work only in the current tab page. That includes the CTRL-W commands, :windo, :all and :ball (when not using the :tab modifier). The commands that are aware of other tab pages than the current one are mentioned below.

Tabs are also a nice way to edit a buffer temporarily without changing the current window layout. Open a new tab page, do whatever you want to do and close the tab page