Click bait is when someone posts an article with a purposely misleading title, like "World's Most Talented Baby!", which is supposed to make you want to click to read more. However, once you click it, the article may just be about a five year old who is really good at singing. Interesting, but not exactly what the title was advertising.
Click bait articles are extremely annoying, as they make you believe that you're going to read something completely contrasting what is actually written on the page. Many creators and authors use this technique to get clicks and views on their Youtube Videos, articles, blogs, or website. Some newspapers do this as well - you can probably recall some headlines that exaggerated the events of the actual news story.