Hello Janet
I am always confused by this expression but I think it's the opposite, as it were, to "intonaco civile" and therefore implies that a single coat is applied (i.e. with no finishing or skim coat), although this is probably standard practice for building exteriors. Note that the material is called render or rendering rather than plaster and there would be no need to specify "exterior" imo. I think you could use the term I have proposed without fear of major retribution, but I would interested to see other comments if / when they arrive.
Best regards
Derek