- Companion banners
- YouTube Mastheads
- Companion Mastheads
- TrueView Video Discovery ads
Explanation: A clickable thumbnail image that accompanies a TrueView in-stream ad. On a YouTube page, it appears next to the ad, in the top right corner (on a desktop computer).Companion banners are optional. They’re also displayed only in certain cases, for example, in the context of a YouTube watch page. They don’t show on embedded players, connected TVs, or game consoles.
Read more here: https://support.google.com/partners/answer/6293542?hl=en