Pop up ads are ads that pop up in their own window when a user goes to a webpage. It blocks the user’s view of the page they are trying to read. They can be moved out of the way or removed completely by closing the window, but this can sometimes take some time. Pop under ads work in the same way but appear under the content the user is trying to read. Both can annoy users as they block their view and can take time to close. However, they can be more effective than banner ads and, as a result, can cost a lot more.