The visual elements and interactions that make up a digital product.
Here's an analogy.
Imagine you’re staying in a hotel. In the best situations, figuring out how the new space works is seamless. You intuitively know how to work the shower, and all of the outlets are within reach when working or resting because someone thought about your needs as a guest when building the room. Good UI design works the same way.
Why does it matter?
A well-designed user interface will enhance the user experience. It provides the necessary visual cues to help a user navigate a product and accomplish a task.
How does it apply?
Digital products require a user interface. It’s the first impression users will have about the product and potentially the business.