Wikipedia
UXR
The User Experience Rating (UXR) is a metric that correlates IT end-user experience with application wait times. UXR is the ratio of wait time to active time, represented as a percentage. It was introduced in 2014 by Logfiller, to describe a key attribute of desktop computing, a feature of their software product, Layer8.
UXR is a concept currently applied to all Windows-based systems, but generically applicable to any device with a measurable UI wait state.