A reference wind velocity usually applied to motion near the ground where the shearing stress is often assumed to be independent of height and approximately proportional to the square of the mean velocity. The friction velocity is, therefore, exactly the velocity for which this square law would be valid. Sutton, O. G. 1953. Micrometeorology. p. 76.
USTAR is the shortname specified in BADM variables (https://ameriflux.lbl.gov/data/aboutdata/data-variables/), whereas ustar is the abbreviation for the variable specified by OzFlux (http://ozflux.org.au/portal/docs/VariableNamesandDefinitions.pdf).
TERN is supported by the Australian Government through the National Collaborative Research Infrastructure Strategy, NCRIS.