User Experience (UX) refers to a person's emotions and attitudes about using a particular product, system or service. It 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.
The international standard on ergonomics of human system interaction, 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.
Early developments in User Experience can be traced back to the machine age that includes the 19th and early 20th centuries. Inspired by the machine age intellectual framework, a quest for improving assembly processes to increase production efficiency and output led to the development of major technological advancements, such as mass production of high-volume goods on moving assembly lines, high-speed printing press, large hydroelectric power production plants, and radio technology to name a few.
Frederick Winslow Taylor and Henry Ford were in the forefront of exploring new ways to make human labor more efficient and productive. Taylor's pioneering research into the efficiency of interactions between workers and their tools is the earliest example that resembles today's user experience fundamentals.
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 used 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 wide use of the term starting in the 1930s., "He suggested that more follow-up in the field would be welcomed by the user, and would be a means of incorporating the results of user's experience into the design of new machines." Use of the term in relation to computer software also pre-dates Norman.
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). Understanding representative users, working environments, interactions and emotional reactions 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.
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