Daisy Chaining aka Waterfall, is the linking of ad networks or ad calls in order to ensure that an ad will be served in order to optimize revenues.
For example, a flat CPM will be assigned to each network and the network with the higher agreed-upon CPM will be first in the daisy chain.
If, for some reason, the network can’t deliver an ad above or equal to that flat price, it passes the ad request back.
The ad request is then redirected to the second network in the chain.
Traditionally, daisy chains are used for remnant inventory.