A computer program that is really simple and easy to use to perform desired tasks is an example of a program that has a good usability rating.
(countable and uncountable, plural usabilities)
usable +"Ž -ity.
usability - Computer Definition
Usability is how easy hardware or software is to operate, especially for the first-time user. Considering how difficult applications and websites can be to navigate through, one would wish that all designers took usability into greater consideration than they do. See hallway testing, good user interface, user interface, RTFM and usability lab.