Cumulative Flow Diagrams (CFDs) are charts that show the cumulative count of work items across different stages of the development process over time. They provide insights into the stability and consistency of the team's workflow, helping identify bottlenecks or workflow imbalances. By monitoring the width of the CFD bands, teams can determine if work is progressing smoothly or if items are piling up in specific areas, which can indicate inefficiencies and prompt further investigation.