What type of flow diagram component is used to reference other flow diagrams?

The correct answer is a subroutine. In flow diagrams, a subroutine is a component used to represent a sequence of steps or a process that has been defined elsewhere, often in another flow diagram. This allows for better organization and modular design within the diagrams. By using subroutines, complex processes can be broken down into simpler, reusable components, enhancing clarity and reducing redundancy.

This approach effectively allows a flow diagram to reference or 'call' another flow diagram where the detailed steps are outlined, making it easier for viewers to follow the overall logic without overwhelming them with every single detail in one diagram. Subroutines can be thought of as functions or procedures in programming, which encapsulate specific tasks and can be reused multiple times within different parts of a program or flow.

The other options represent different components of flow diagrams but do not serve the purpose of referencing external diagrams. Input/output components indicate where data is received or sent, process components depict operations or actions, and decision components represent branching logic based on a yes/no or true/false condition. Each of these components serves a distinct role, but only the subroutine allows for cross-referencing of flow diagrams.