A Data Flow Diagram (DFD) is a graphical representation of the flow of data through a system. It shows the input and output data to the system, where data is stored, and how data is processed. DFDs do not show the timing or sequence of data processing. There are several elements to a DFD including processes, data stores, entities, and data flows. Processes transform input data into output data. Data stores represent where data is stored. Entities are sources or destinations of data outside the system. Data flows show the direction of data movement. DFDs can be physical or logical and have different levels of abstraction.