Some operations require a double click, meaning that you must click a mouse button twice in rapid succession. Shift clicking refers to clicking the mouse button while holding the Shift key down.

(n) (1) The pressing down and rapid release of a mouse button.

(2) In the World Wide Web advertising industry, selection of a banner ad by a user. The effectiveness of Web advertisements are measured by their click-through rate - how often people who see the ad click on it.