Final answer:
In Data Flow Diagrams (DFDs), a rectangle symbol can represent an external entity in a Context Diagram and a process in lower-level DFDs.
Step-by-step explanation:
The symbol that can be either an entity or a process depending on the type of Data Flow Diagram (DFD) is the rectangle. In a Context Diagram, which is a high-level DFD, rectangles represent external entities, which are system interactors outside of the system boundary. However, in lower-level DFDs, rectangles are used to represent processes, which are the functions or transformations that data undergo inside the system.
Understanding the context of each rectangle is essential as you switch between different levels of DFDs. In a DFD, arrows represent the data flow between entities and processes, and circles (or rounded rectangles) usually depict data stores, where data is held for later use.