What is web site usability?

Usability refers to the user experience when interacting with your website.

A website that is usable is one that makes everything clear and simple to understand for the user. Although it is impossible to make a website that will be clear and efficient for every user, it is possible to make a site that will present the user with a minimum amount of confusion.

Going one step beyond this, planning for errors that may occur when a user is interacting with your website and developing smart ways of handling these errors is called contingency design, and together usability and contingency design can result in a user being satisfied with their experience on your website.