User Experience (often abbreviated to UX) is a blanket term for all the factors that influence a user's perception of a product or service.
With that, UX design concerns itself with the design of the experience of acquiring the product, using the product and the aftercare.
The goal of User Experience design is to create positive, emotional responses and reducing negative responses. Because these largely determine whether the overall product or service is considered to be ‘good’ or ‘bad’.
The image above shows the workflow of a User Experience designer. This flow iterates as long as there is a budget 😉.
UX design as a profession
Because a UX professional often oversees several disciplines in order to come to a more successful product, it is considered to be a directorial professional role.
The professional often oversees the project's graphic design, user interface design, copywriting and so on. Therefore, a UX designer is ought to have expertise in multiple areas such as design, psychology and marketing.
What UX is not
User Experience is not User Interface design (UI) nor is it usability. UI is definitely a part of UX yet refers mostly to the visual and technical ways that users interact with the product. Usability is defined as a measure of ease-of-use of a product.
What is 'User Experience'?
The Oxford Dictionary gives a rather great, one sentence description of User Experience:
The overall experience of a person using a product such as a website or a computer application, especially in terms of how easy or pleasing it is to use.