Final answer:
A pop-up ad appears in a new window on top of the current web page, while a pop-under ad opens behind the current browser window or tab and remains hidden until the user closes or minimizes the window.
Step-by-step explanation:
A pop-up ad is a type of online advertisement that appears in a new window or tab and is displayed on top of the current web page. It typically grabs the user's attention by interrupting their browsing experience. On the other hand, a pop-under ad is an advertisement that opens in a new window behind the current browser window or tab. It remains hidden until the user closes or minimizes the current window.
An example of a pop-up ad is when a website opens a new window displaying an ad for a product or service. This ad may be triggered when the user enters the site or clicks on a specific link. On the contrary, an example of a pop-under ad is when a user closes their browser and then notices a new window or tab with an advertisement that was hidden during their browsing session.
In summary, the main difference between pop-up and pop-under ads is their behavior and visibility. Pop-up ads are displayed on top of the current web page, while pop-under ads are hidden behind it and only become visible when the user closes or minimizes the current window.