What is a Sub-flow in MuleSoft?

A Sub-flow in MuleSoft is essentially a reusable set of operations designed to encapsulate logic that can be invoked by multiple flows. This reusability is a key feature that allows developers to maintain consistency across different flows and reduces redundancy in design. By defining a Sub-flow, developers can implement a portion of their integration logic once and call it wherever necessary, which enhances modularity and simplifies maintenance.

Sub-flows can be created to perform specific tasks such as data transformation, calling an API, or handling a particular workflow step, and they're typically invoked within other flows using the flow-ref component. This capability to reuse operations not only saves time in development but also helps in managing extensive projects more efficiently.

Other options don't accurately capture the essence of a Sub-flow. For instance, a flow that cannot be reused doesn't align with the core functionality of a Sub-flow, which is specifically designed for reuse. A set of operations for integration is too vague and does not specify the reusability aspect. Lastly, while error handling is a vital part of flow design, it pertains to different constructs in MuleSoft, not specifically to the definition of a Sub-flow.