Act break
An act break is the structural turning point where one act ends and the next begins — a decisive shift that raises the stakes and changes the direction of the story. In television it is also the literal break for a commercial, written to leave the audience on a hook that survives the ad.
In feature structure, act breaks are the major hinges: the end of Act One commits the hero to the journey, the midpoint and end of Act Two escalate and then collapse, and the climax resolves it. They are felt by the audience even when nothing on screen announces them.
In television the act break is concrete: it is where the show cuts to commercial, so each break is engineered as a cliffhanger or reveal strong enough to hold viewers through the break. Network hours are built around a fixed number of these.