Attract mode
Also said as Demo mode, Advertise mode, Self-playing demo
What a game does when nobody is playing: shows itself. Arcade cabinets looped their title, scores and a demo that played itself, to pull people in from across the room. This site's home page is doing the same thing right now.
A silent machine in a loud room earns nothing. The demo shows what the game is in seconds, and it does so to people who weren't looking for it. Any screen that waits for a stranger needs the same idea.
Say it
“After 20 seconds on the title screen, play a recorded run with sound off and a blinking press start. Any input drops the player straight into a new game.”
Where you’ve seen it
Pac-Man's attract mode introduces its four ghosts on screen, by character and by nickname, then shows a demo chase.
Not to be confused with trailer
A trailer is an edited film about the game. An attract mode is the game itself, running where you can step in and take over.