UI / Usability 5 Quality Components

Learnability

How easy is it for users to accomplish basic tasks the first time they encounter the design? 

Efficiency

Once users have learned the design, how quickly can they perform tasks?

Memorability

When users return to the design after a period of not using it, how easily can they reestablish proficiency?

Errors

How many errors do users make, how severe are these errors, and how easily can they recover from the errors?

Satisfaction

How pleasant is it to use the design?

UI / Definition Of Usability

Effectiveness

Accuracy and completeness with which users achieve specified goals

Efficiency

Resources expended in relation to the accuracy and completeness with which users achieve goals

Satisfaction

Freedom from discomfort, and positive attitudes towards the use of the product

Context of use

Users, tasks, equipment (hardware, software and materials), and the physical and social environments in which a product is used