User interface design
Not to be confused with graphic/visual design, user interface design aims to create effective, intuitive interfaces and make the user’s experience of that interface as straightforward and efficient as possible, whether it be in the cockpit of an A380 or a page on your website.
User Interface Design involves the design and layout of the objects on a website’s interface, and ensuring that they are useful, usable and reliable for all users - often an involved process.
Sometimes it is preferable to ask the user to learn how to use an interface (eg software), but on the Web the user interface almost exclusively has to be readily and instantly usable, which means the user can use the site without training.
A good user interface takes advantage of the strengths of its medium and avoids its weaknesses. One advantage of Web interfaces is the ability to re-size the text to suit your eye-sight. If the Website is correctly designed, it will tolerate this change and allow you to continue using it. Go ahead and make the text of this website larger. You will see that you have to make the text very large until the layout "breaks". Not all websites are designed with this important but often overlooked feature.
User interface design with a strong focus on usability is also referred to as user-centred design. User interface design is usually the pre-cursor to visual design.