Functional Description of Software is a document that describes the functions and features of a software system or application. It typically outlines the tasks the software will be able to perform, the inputs and outputs, and the conditions that must be met for the software to operate correctly. It is usually written from the perspective of a user, rather than a developer, and is used to define the scope of a software project. The main types of Functional Description of Software are: 1. User-Level Functional Description: This type of description outlines the user interface and the expected user experience of the software. It defines the functions the user will be able to perform, the input and output of the system and the conditions under which the software will operate correctly. 2. System-Level Functional Description: This description outlines the underlying architecture of the software, the components it is made up of, and how they interact to provide the functionality of the system. It is usually written from a technical perspective and is used to define the scope of a software project. 3. Process-Level Functional Description: This description outlines the processes and tasks that the software is designed to perform, the inputs and outputs, and the conditions that must be met for the software to operate correctly. It is written from a functional perspective and is used to define the scope of a software project.