In online advertising, an interstitial is an ad that is displayed before or after the expected content. For example, if a pop-up that loads before the actual content of a page is displayed, then it is considered an interstitial. Interstitials can be small-sized or full-page and interrupt the user, exposing him to a promotional message with the purpose of convincing him to make a profitable action – buy, download, subscribe and so on.
Interstitials are part of the interruption marketing strategies and although they may be effective in generating conversions. They can also lead to resentments and negative user reactions, especially when displayed too often.