The term used to describe a system or process that is easy to use. Most often used to describe a discipline of specialists focused on creating usable graphical interfaces. Also used to describe formal or informal tests with actual users, often in a lab setting.
How easy a product is to use. It has been defined as: "the effectiveness, efficiency and satisfaction with which a specified set of users can achieve a specified set of tasks in a particular environment".
Ability of a system to be used [easily or efficiently] Usability is different than utility (ability of something to satisfy a need). The word usability arises in relation with the Human-Computer interface studies. The interface of a program or of a web site can be useful because it performs the whole range of operations specified, but can be of low usability, for example, due to a high complexity that makes it difficult to be used efficiently for non-trained people.