Overlay

An overlay is a graphic layered on top of live video. It usually has a transparent background, so only the graphic itself shows over the picture — the rest of the frame remains the live feed. Lower thirds, scoreboards, sponsor bugs, tickers and up-next teasers are all overlays.

The key idea is that an overlay is layered: it appears, updates and disappears independently of the video beneath it. On modern streams overlays are built as web pages and rendered by a browser source in software like OBS or vMix, which means their content can change live without touching the underlying feed.