Casting lets a viewer start content on a phone or tablet and push it to a big screen - Chromecast and Google Cast, Apple AirPlay - while the mobile device becomes a remote control. Crucially, in the common model the TV device fetches and plays the stream itself; the phone just hands off the session, so quality and DRM are handled by the receiver.
That hand-off makes casting more than a UI feature: the receiver must support the right protocols, codecs, and DRM, the session and entitlement must transfer cleanly, and playback position must stay in sync so the viewer can reclaim control on the phone. Casting is part of the broader continuity story of letting a viewer move seamlessly across screens.
