I'd agree with the above - "icing conditions" are when ice can form, freezing conditions are when water (typically) can freeze. I doubt there will be any single definitive definition, since things like the indicated temperature will differ from aircraft to aircraft (depending if the system indicates TAT or SAT, for one example) I know of aircraft where there are different definitions for icing conditions in flight and on the ground, and where the icing conditions for the engine are different again.