Wiktionary
n. 1 The state or condition of being usable. 2 The degree to which an object, device, software application, etc. is easy to use with no specific training.
Wikipedia
Usability is the ease of use and learnability of a human-made object. In software engineering, usability is the degree to which a software can be used by specified consumers to achieve quantified objectives with effectiveness, efficiency, and satisfaction in a quantified context of use.
The object of use can be a software application, website, book, tool, machine, process, or anything a human interacts with. A usability study may be conducted as a primary job function by a usability analyst or as a secondary job function by designers, technical writers, marketing personnel, and others. It is widely used in consumer electronics, communication, and knowledge transfer objects (such as a cookbook, a document or online help) and mechanical objects such as a door handle or a hammer.
Usability includes methods of measuring usability, such as needs analysis and the study of the principles behind an object's perceived efficiency or elegance. In human-computer interaction and computer science, usability studies the elegance and clarity with which the interaction with a computer program or a web site ( web usability) is designed. Usability differs from user satisfaction and user experience because usability does not directly consider usefulness or utility.
Usage examples of "usability".
Whenever a gate is recharging, the numerals will appear, counting down the time to usability in minutes and seconds, and for the Earth gate in hours as well.
The standard set of permissions on system files and directories provide a reasonable degree of security without interfering with the computer's usability.