A click is an action performed by a user when they activate a link or button on a website or application by clicking on it with a mouse, trackpad, or touch screen. Clicks are often used to navigate to a new page or trigger an action, such as submitting a form or making a purchase.

In the context of online advertising, a click is an event that occurs when a user clicks on an ad, such as a display ad or search ad. This can be used to measure the effectiveness of an ad campaign, as the number of clicks can indicate how many people are interested in the product or service being advertised.

In addition to measuring the number of clicks, advertisers and marketers can also track other metrics related to clicks, such as click-through rate (CTR) and cost-per-click (CPC). CTR is the ratio of clicks to impressions, or the number of times an ad is displayed, while CPC is the cost of an ad campaign divided by the number of clicks it generates.