One rich source of information is Wikipedia: https://en.wikipedia.org/wiki/Tab_(interface) On your Mac, there is a "tabs" bar along the top of the browsing window, below the top menu bar. Each page open in the current window is represented by a tab, and the tab shows the site icon and the first part of the page title. On iPhone or iPad, the tabs bar appears just below the devices top bar. By the way, were you just curious or was there a problem such as a tab crashing?