Both terms are used in the United States, but the plural form is more common in American English, while in contrast, British English uses only the singular form.
bˈoʊθ tˈɜːmz ɑːɹ jˈuːzd ɪnðə juːnˈaɪɾᵻd stˈeɪts, bˌʌt ðə plˈʊɹɹəl fˈɔːɹm ɪz mˈoːɹ kˈɑːmən ɪn ɐmˈɛɹɪkən ˈɪŋɡlɪʃ, wˌaɪl ɪn kˈɑːntɹæst, bɹˈɪɾɪʃ ˈɪŋɡlɪʃ jˈuːsᵻz ˈoʊnli ðə sˈɪŋɡjʊlɚ fˈɔːɹm.