Usability concerns the 'ease of use' of a product or system. The international standard, ISO 9241-11, provides guidance on usability and defines it as:
"The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use."
Hence one can see that usability concerns:
- Effectiveness - can users achieve what they need to do using the product?
- Efficiency - how much effort (e.g. time) does it require?
- Satisfaction - how do they feel about their interaction with the product?
However, these factors are affected by:
- The users - who is using the product? e.g. are they highly trained and experienced users, or novices?
- Their goals - what are the users trying to do with the product - does it support what they want to do with it?
- The usage situation (or 'context of use') - where and how is the product being used?
Usability ought not to be confused with 'functionality', however, as this is purely concerned with the functions and features of the product and has no bearing on whether users are able to use them or not. Greater functionality does not mean improved usability!