Value
Definition: The regard that something is held to deserve; the importance, worth, or usefulness of something.
The value of a given software in terms of UX is what the User perceives they are getting from using the software.
Usefulness
Definition: The content and function of the software fulfill a need for the user.
This is the power of the software.
Desirability
Definition: Wanted or wished for as being an attractive, useful, or necessary course of action.
This is the *oh-so-pleasant-to-use* feeling you get when you interact with a well built product.
Accessibility
Definition: Able to be reached, used or entered by people who have a disability.
How easy is your software to use? Could I use it with my eyes closed? Could I use it with only one hand? One finger? Can a colorblind person easily see it?
Findability
Definition: The ease with which information contained within a software can be found, both from outside the software and by users already using the software.
Everything important should be easily findable by the user.
Credibility
Definition: The quality of being convincing or believable.
Trust is paramount to users. They need to know that you will be responsible with their information, and that your software does what it claims to do, reliably.
Usability
Definition: The capacity of a system to provide a condition for its users to perform the tasks safely, effectively, and efficiently while enjoying the experience.
This is how well you’ve executed all of the above, and how all of those aspects fit together.