An overlay refers to a visual element displayed on top of a video feed or livestream. It is used to provide additional information or graphics that enhance the viewing experience. In the context of livetagging and sports statistics, overlays are commonly used to display real-time data, such as scores, player stats, and game updates. Overlays in vMix can be customized and designed to match the branding or theme of the livestream. They are an effective way to engage viewers and provide them with relevant information during the broadcast.