A companion ad is a secondary advertisement that is displayed in conjunction with a primary ad, such as a video ad. Companion ads are often used to provide additional information or context about the primary ad, or to promote related products or services.

Companion ads may be displayed in a variety of formats, including banner ads, text ads, or interactive ads. They may appear alongside the primary ad on the same webpage or app, or they may be displayed in separate locations.

Companion ads are often used in online video advertising, where they can be displayed as overlays or as banners alongside the video player. They may also be used in other types of digital advertising, such as display advertising or mobile advertising. Companion ads are typically used to complement the primary ad and to provide additional information or context to the viewer.