(v) To tap on a mouse button, pressing it down and then immediately releasing it. Note that clicking a mouse button is different from pressing (or dragging) a mouse button, which implies that you hold the button down without releasing it. The phrase to click on means to select (a screen object) by moving the mouse pointer to the object’s position and clicking a mouse button.
(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.