[¦in·tər¦nash·ən·əl ′tem·prə·chər ‚skāl] (thermodynamics) A standard temperature scale, adopted in 1990, that approximates the thermodynamic scale, based on assigned temperature values of 17 thermodynamic equilibrium fixed points and prescribed thermometers for interpolation between them. Abbreviated ITS-90.AcronymsSeeios telephony service