Desirability deals with feelings and emotions. It is focused on making users to get something. Desirability, not equal usability. We can hanker to get the new thing. But no matter how desirable the item appeared if it’s frustrated in usability!
Desirability provides users with an enjoyable experience (usability) and provides a certain “wow factor” that creates an emotional bond with the user, compelling them to keep using the product because it offers them pleasure, which is a reward in and of itself.

Usability means how easily user interacts with a product, how effectively and efficiently the user can achieve required goals.

Accessibility is about to ensure that the product is accessible for people regardless of ability or disability. Accessibility enables everyone to use the products . This includes people with low vision, color blindness, hearing difficulty, mobility problems, cognitive disabilities, the young and the old. By taking these needs into account, the designer can cater for the true diversity of users.