From a UX perspective, scenarios, task flows, and use cases are all tools/processes that can be used to understand and design the interactions that users will have with a product or system.
Scenarios are narratives that describe a specific user’s interactions with a product or system. They are often used to help designers understand how users will complete tasks and achieve goals within the context of a larger workflow.
Task flows are diagrams that show the steps a user must take to complete a specific task. They are often used to help designers understand the steps involved in a particular workflow and identify any potential points of confusion or complexity.
Use cases are descriptions of how a system or product will be used by a specific user or group of users to achieve a specific goal. They are often used to help designers understand the interactions that users will have with a product or system, and to identify any requirements or constraints that must be taken into account during the design process.
In summary, scenarios and use cases are more focused on the context and goal of the user, while task flows are more focused on the step-by-step process of completing a task. All three can be used together to provide a more comprehensive understanding of the user’s experience with the product.