Usability testing, a non-functional testing technique that is a measure of how easily the system can be used by end users. It is difficult to evaluate and measure but can be evaluated based on the below parameters:
Level of Skill required to learn/use the software. It should maintain the balance for both novice and expert user.
Time required to get used to in using the software.
The measure of increase in user productivity if any.
Assessment of a user's attitude towards using the software.