||This article possibly contains original research. (December 2010)|
User experience (UX) involves a person's behaviors, attitudes, and emotions about using a particular product, system or service. User experience includes the practical, experiential, affective, meaningful and valuable aspects of human-computer interaction and product ownership. Additionally, it includes a person’s perceptions of system aspects such as utility, ease of use and efficiency. User experience may be considered subjective in nature to the degree that it is about individual perception and thought with respect to the system. User experience is dynamic as it is constantly modified over time due to changing usage circumstances and changes to individual systems as well as the wider usage context in which they can be found.
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". According to the ISO definition, user experience includes all the users' emotions, beliefs, preferences, perceptions, physical and psychological responses, behaviors and accomplishments that occur before, during and after use. The ISO also list three factors that influence user experience: system, user and the context of use.
Note 3 of the standard hints that usability addresses aspects of user experience, e.g. "usability criteria can be used to assess aspects of user experience". The standard does not go further in clarifying the relation between user experience and usability. Clearly, the two are overlapping concepts, with usability including pragmatic aspects (getting a task done) and user experience focusing on users’ feelings stemming both from pragmatic and hedonic aspects of the system. Many practitioners use the terms interchangeably. The term usability pre-dates the term user experience . Part of the reason the terms are often used interchangeably is that, as a practical matter, a user will at minimum require sufficient usability to accomplish a task, while the feelings of the user may be less important, even to the user herself. Since usability is about getting a task done, aspects of user experience like information architecture and user interface can help or hinder a user's experience. If a website has "bad" information architecture and a user has a difficult time finding what they are looking for, then a user will not have an effective, efficient and satisfying search. Usability can essentially be considered a subfield of user experience. Put another way, the feelings of the user generally depend upon having a successful experience in accomplishing the task at hand. Users have been known to use systems with sub-optimal user experiences and even "bad" usability, in order to accomplish their task goals .
According to Jim Miller, principal of Miramontes Computing, user experience "encompasses much more than the traditional 'user interface' issues, such as screen design and command structure. Rather, it's a broad collection of user-centric issues that cut through the full extent of a project."
The term user experience was brought to wider knowledge by Donald Norman in the mid-1990s. He never intended the term "user experience" to be applied only to the affective aspects of usage. A review of his earlier work  suggests that the term "user experience" was coined to signal a shift to include affective factors, along with the pre-requisite behavioral concerns, which had been traditionally considered in the field. Many usability practitioners continue to research and attend to affective factors associated with end-users, and have been doing so for years, long before the term "user experience" was introduced in the mid-1990s . In an interview in 2007 Norman discusses the widespread use of the term "user experience" and its imprecise meaning as a consequence thereof.
Several developments affected the rise of interest in the user experience:
The field of user experience represents an expansion and extension of the field of usability, to include the holistic perspective of how a person feels about using a system. The focus is on pleasure and value as well as on performance. The exact definition, framework, and elements of user experience are still evolving.
User Experience of an interactive product or a web site is usually measured by a number of methods, including questionnaires, focus groups, and other methods. A freely available questionnaire (available in several languages) is the User Experience Questionnaire UEQ. The development and validation of this questionnaire is described in 
Google Ngram Viewer shows an earliest use of the term "User Experience" as 1963. Use of the term in relation to computer software also pre-dates Norman.
The University of Waterloo Stratford Campus held a UX bootcamp on its campus in November 2013.  It had teams develop solutions to a given real life problem using the 5 planes of UX, which are surface, skeleton, structure, scope and strategy.
Many factors can influence a user's experience with a system. To address the variety, factors influencing user experience have been classified into three main categories: user's state and previous experience, system properties, and the usage context (situation). Studying typical users, contexts, interactions and resulting emotions help in designing the system.
Single experiences influence the overall user experience: the experience of a key click affects the experience of typing a text message, the experience of typing a message affects the experience of text messaging, and the experience of text messaging affects the overall user experience with the phone. The overall user experience is not simply a sum of smaller interaction experiences, because some experiences are more salient than others. Overall user experience is also influenced by factors outside the actual interaction episode: brand, pricing, friends' opinions, reports in media, etc.
One branch in user experience research focuses on emotions.This includes momentary experiences during interaction: designing affective interaction and evaluating emotions. Another branch is interested in understanding the long-term relation between user experience and product appreciation. The industry sees good overall user experience with a company's products as critical for securing brand loyalty and enhancing the growth of customer base. All temporal levels of user experience (momentary, episodic, and long-term) are important, but the methods to design and evaluate these levels can be very different.