"User experience" encompasses all aspects of the end-user's interaction with the company, its services, and its products.'      Don Norman and Jakob Nielsen

"... User’s perceptions and responses include the user’s emotions, beliefs, preferences, perceptions, comfort, behaviours, and accomplishments that occur before, during and after use."      ISO

'...focuses on having a deep understanding of users, what they need, what they value, their abilities, and also their limitations."     usability.gov

Peter Morville's honeycomb presents elements of user experience. In addition to the efficiency and accessible "use" of a service, system, or object, UX studies look at what users think and feel - is it "desirable" and "valuable"? Morville  & Karagianni

A UX Research Cheat Sheet from Nielsen Norman Group stresses user research can be done at any point. Explore the complete list of methods and activities in four categories.