VP9 is a royalty free video compression format (also known as a video codec).
VP9 was open sourced by Google and is seen by Google as the successor of VP8.
VP9 takes considerably more processing power than VP8, but produces better quality on the same bitrate (or lower bitrate for the same quality). VP9 also supports SVC.
Today, VP9 is being commercially used in YouTube, Google Meet, Jitsi Meet and other applications.
VP9 is said to be on par with H.265 (the successor of H.264).