"Let's say your Internet browser (Safari, Chrome, Firefox, Opera) is set to full screen mode," so begins the latest from John Carter. He goes on, "You have been browsing in the PMUG website. You decide you want to check out the latest news in the Newsletter. When you click on the Newsletter button in the navigation bar at the top of the window, the PMUG website you were looking at is seemingly replaced with the Newsletter page.
"Now you want to get back to the PMUG site. Do you go to the address bar and enter in the PMUG URL? No! Do you quit the browser and start all over again? No! The PMUG website page is still open and hiding behind the Newsletter page. All you need to do is close the window with the Newsletter (Cmd-W) and the PMUG website page is revealed.
"If you are using Firefox, Opera, or Chrome, you may have your preferences set up to open a link in a new tab in the current window instead of opening a new window. Using Cmd-W closes the tab with the page that is being displayed in the window and reveals the page in the previous tab.
"So how many browser windows do you have open at one time? Clicking on Window in the menu bar will show you: (Chrome browser example in Snow Leopard) The check mark identifies the current window. All other entries in that section (at the bottom) are more open browser windows. Clicking on one of them displays that window.
(Chrome browser example in Snow Leopard)
"Another way to identify open windows is to right click (Ctrl-click) on the browser icon in the dock. The pop-up menu shows the open windows in the top section of that menu:
(Chrome browser example in Snow Leopard)
"If you have multiple tabs open to different web pages in only one browser window, you will see only one window in the above two examples with the name of the page in the current tab."
Thanks, John, for more helpful information.