What clickbait means
Dictionaries define the word broadly. The Cambridge Dictionary describes clickbait as an internet story, title or image that is intended to attract attention and encourage people to click on a link. The German Duden speaks of a headline, image or teaser meant to lure people into clicking and reading or watching on. The word itself combines click and bait. On that definition, almost any well-crafted headline would count. In marketing and in platform guidelines the sense is narrower: the click is won with something the page then fails to deliver.
Facebook put it this way on 25 August 2014, when it announced it would show fewer such posts: click-baiting is when a publisher posts a link with a headline that encourages people to click to see more, without telling them much about what they will see. In an initial survey, according to Facebook, people preferred headlines that helped them decide whether to read the full article before clicking 80% of the time.
Google uses the word in its recommendations for Google Discover. It asks publishers to avoid clickbait and similar tactics that artificially inflate engagement, and names two of them: misleading or exaggerated details in preview content (the title, snippets or images), and withholding crucial information needed to understand what the content is about. In the same list it asks publishers to avoid sensationalism that plays on morbid curiosity, titillation or outrage.
A curiosity gap is not the same as deception. In 1994 the researcher George Loewenstein described curiosity as a form of deprivation that arises when someone perceives a gap in their knowledge or understanding. A good headline may open that gap. The difference lies in what happens after the click. If the page closes the gap with what the title promised, the reader got what they came for. If it does not, or closes it with something smaller, it is clickbait. Loewenstein also noted curiosity's tendency to disappoint once it is satisfied, which makes an inflated promise all the more noticeable.