- marketplaces has demand and supply

- demand are the buyers (people who spend the money)

- supply are the sellers (people who has the goods)

- online digital ads are typically sold and bought in a marketplace style system

- demand are the advertisers

- supply are people with the "goods", in this case, ad placement slots such as websites, newsletters, apps, app stores.. anywhere the advertiser can find audience and put an ad.

- demand side platform is a platform for the advertisers to connect with the supply.