Define User Interface and explain why it is required in Software Engineering.

User Interface (UI) is the space where interactions between humans and machines occur. It involves everything designed into an information device with which a user may interact, including display screen, keyboard, mouse, the appearance of a desktop, illuminated characters, help messages, and how an application program or a website invites interaction and responds to it.

In Software Engineering, UI is required for the following reasons:

1. User-Friendly Interaction: A good UI makes it easy for users to interact with the software. It provides a simple and convenient way to access the functions of the software, making it user-friendly.

2. Efficiency: A well-designed UI increases the efficiency of the user. It helps them to complete tasks quickly by providing intuitive navigation and easy-to-understand instructions.

3. Satisfaction: A good UI can lead to increased user satisfaction. If users find the software easy to use and pleasing to the eye, they are more likely to use it and recommend it to others.

4. Reduces Errors: A well-designed UI can also help to reduce errors. By providing clear instructions and preventing users from making certain mistakes, a good UI can help to improve the overall performance of the software.

5. Competitive Advantage: Finally, a good UI can provide a competitive advantage. If two software applications have similar functionality but one has a better UI, users are more likely to choose the one with the better UI.