Usability and User experience (UX) are defined in an international standard, ISO 9241.

Usability concerns the 'ease of use' of a product or system. ISO 9241-210, which deals with the user-centred design of interactive systems, defines it as follows:

"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."

Whether a product has good or bad usability can therefore be determined by looking at:

• 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?

User experience is defined by ISO 9241-210 as follows:

"A person's perceptions and responses resulting from the use and/or anticipated use of a product, system or service."

This builds on the 'satisfaction' element of usability by including user emotions, beliefs, preferences, perceptions, physical and psychological responses, behaviours and accomplishments that occur before, during and after use.

When working with usability and user experience it is important to consider that they 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?
• Their attitude to the product - how do they perceive it's capabilities, aesthetic appeal, brand image, etc?
• The usage situation (or 'context of use') - where and how is the product being used?

It is worth noting that greater functionality (or more features) doesn't necessarily mean improved usability and a better user experience. This can only happen if new functionality actually improves how users interact with, and perceive, the product.

The definition of accessibility is found in another part of the same standard, ISO 9241-171. For a product to be usable by all, a prerequisite is that everyone must have the possibility to access it either directly or through use of assistive technology. ISO 9241-171 defines accessibility as:

"The usability of a product, service, environment or facility by people with the widest range of capabilities."