User Experience (UX) is software to be installed on our cultural systems:

Where we work, on our corporate culture systems.
Where we govern, on our community and governance systems.
Where we build, on our constructive systems.
Where we educate, on our educational, pedagogical, instructive systems.

Those are complex adaptive systems of the many social organisms that pervade our living experiences. (Wikipedia entry on CAS.) (The Santa Fe Institute.) 
Similar to how other technologies evolve, UX is appropriately seen as referring to the latest or current installation of of this cultural software. For those of us who work in the field, we might view earlier installations as “usability”, “usability engineering”, or “human-computer interactions”. It is to say – and to see – that we adapt beyond those earlier installations by the fact that the diverse cultural systems in which they began have themselves adapted.

It is also important to observe that there are flavors of this cultural software that vary by locale. For instance, many of us work in groups who tend to identify more with “information architecture“, or “interaction design“, or “interactive strategy”. These are simply labels, and we mustn’t be foolish enough to fall for the labels when there is the core of a dynamic organism here to be appreciated. “User Experience” is simply the current moniker for something many of us believe to have larger value.

It is a delight to work in a field that reflects a current of social adaptation – even when the daily fits and starts of how we practice and define ourselves is such a predictable distraction. It makes me feel human to see how our practice is a modern amalgum of tool-building and democracy. It also lets me see the reflection of how organisms advance by accumulating the results of our insights and efforts on a daily basis.

The field of User Experience marks the adaptation of our cultural systems to improve and advance the quality of their interactions, the efficiency and efficacy of their commerce, and the resilience of their communities.