User Experience describes the total interaction or experience a user has with your design or product including ownership, usage, perceptions and feelings with and about the design. Does the product meet their needs? Is it easy to use? Is it a joy to use? Does it make them smile?
ISO 9241-210 defines user experience as "a person's perceptions and responses that result from the use or anticipated use of a product, system or service". So, user experience is subjective and focuses on the experience a user has with your design. User experience is subjective because it involves the social, emotional, cognitive or cultural triggers your user might bring to the design experience before, during and after use. The totality of individual experiences and overall impressions make up a "user experience". ISO lists three factors that influence user experience: system, user and the context of use.
User experience is dynamic, because it changes over time as the user interacts with the product or is impacted by changes in attention, memory, or the physical or social environment, for example. The mechanics of how your experience plays out for the user are dynamics that can be studied with user research or usability testing, and positively improved. Our usability consulting expertise in these dynamics gave us our name: Experience Dynamics.
User experience has its roots in the field of Cognitive Science (human factors or ergonomics) and the branch called Human Computer Interaction (HCI). We call HCI the Science of Usability. User Experience Design involves leveraging insights from psychology and computer science primarily with large doses of anthropology, sociology, neuroscience and linguistics to improve the end user experience. User Experience designers often refer to designing interactions, which is why the term Interaction Design or Information Architecture is also used.
Poor user experience can result in eroded loyalty and trust with your end users. As a result website usability can suffer with lower customer conversion, for example. Good user experience such as 'a user had a good mobile user experience with the iPhone' can increase sell-ability, intent to purchase and intent to return. e.g. A recent study by Right Now (2010) showed that 85% of customers say will pay premium price for great customer experience.
See The Importance of User Experience poster.