This page will provide a little background on web site usability as a part of the overall user experience.
What is User Experience Design?
User experience design is the design of the overall experience of users, not just their web experience. Think of this as a holistic thing that goes way beyond just the web site, though the web site is a key element of the experience of any library, company, or organization.
"User experience" encompasses all aspects of the end-user's interaction with the company, its services, and its products. - Nielsen Norman Group https://www.nngroup.com/articles/definition-user-experience/
What is Web Site Usability?
Web site usability is the ease of use (or lack thereof) of a web site. This is measurable via web site usabiity testing with users. Testing can be done quickly and efficiently with small numbers of users to great benefit.
"Test, edit, repeat." - Stephanie Willen Brown, Simmons College Library & Information Science Professor & Director, Park Library, UNC School of Media & Journalism
According to Jakob Nielsen, usability is defined by 5 quality components: learnability, efficiency, memorability, errors, and satisfaction. From "Introduction to Usability" https://www.nngroup.com/articles/usability-101-introduction-to-usability/
needless words" - Steve Krug