The process of opening multiple tabs in a browser, usually by holding the Ctrl key and clicking on a link. (Also by selecting "Open Link in New Tab" from the right-mouse-click pop-up menu.)
It is a way of opening a new web page without losing your location in the current page.
Example (as mentioned on xkcd): Go to
TvTropes and then Ctrl-click on the blue links that you want to investigate further. When you get to the bottom of the current page, you'll have a plethora of tabbed topics to investigate further.