Great question — answering as the UphillTech team:
According to an article from TV Guide , the four quadrants are split according to male or female and old or young. From another site about audience demographics, it appears the the old-young split is made at age 25. Edit: Here's an image I found on a site for independent filmmakers :
Full answer by FredH: https://movies.stackexchange.com/a/11438 (CC BY-SA 3.0).
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