Which principle of good UX and UI design emphasizes the importance of making websites usable for visually or mobility impaired users?

The principle that emphasizes the importance of making websites usable for visually or mobility-impaired users is accessibility. This concept focuses on designing web content and interfaces in a way that allows all people, regardless of their abilities or disabilities, to access and use the website effectively. Accessibility includes practices such as providing text alternatives for non-text content, ensuring that navigation is possible via keyboard for those who cannot use a mouse, and ensuring that the site can be used with screen readers.

Incorporating accessibility means addressing the needs of users with various types of impairments, which leads to a more inclusive user experience. When a website is accessible, it not only benefits users with disabilities but also improves overall usability, as many accessible design practices contribute to a better experience for all users.

Usability, while related, focuses more broadly on how easy and satisfying a website is to use, without specifically addressing the needs of differently-abled users. Engagement pertains to how well a site captures and maintains user interest, and aesthetics is about the visual appeal of a website. These aspects are important but do not specifically highlight the necessity of making a website usable for individuals with disabilities. Hence, accessibility stands out as the critical principle in this context.