It's a screenshot! I'm on Firefox and I downloaded an add-on called "ScreenGrab!" where when I right click on a page, it gives me several options on how I want to capture that screenshot.

Another way to do it without downloading anything is to simply press Ctrl+Prnt Scrn (latter button should be on the top right of your keyboard). This copies an image of whatever's on your desktop and you can paste it into Paint, Paint Shop Pro, ImageReady, etc, just whatever image program you use.

I sometimes take screenshots to show the tech team an issue that I'm having with the site that would otherwise be difficult to describe, so that's one use for it ;)