Adverts that are disguised as other kinds of content or navigation, in order to get you to click on them.
Softpedia is a popular software download site. One of their sources of revenue is display advertising. They often run advertisements that look like a download button, tricking users into clicking on the ads rather than getting the thing they wanted. In the screengrab below, the real download link is at the top left of the page. The disguised ads are highlighted in red.