A waterfall chains multiple data providers in order β Provider A, then B, then C, then D β with each one filling gaps the previous couldn't cover. A well-built waterfall typically lifts email and firmographic coverage from around 20% to over 80%.
Clay is the reference orchestrator for this pattern. Explorium and ZoomInfo GTM.AI extend it with server-side batch processing.
The cost logic is important: always put the cheapest provider first and the most accurate (and most expensive) last. You only spend premium credits on records the cheap providers couldn't complete.