There is no hard-and-fast distinction between them, and these categories overlap to a considerable degree.
ðɛɹ ɪz nˈoʊ hˈɑːɹdændfˈæst dɪstˈɪŋkʃən bᵻtwˈiːn ðˌɛm, ænd ðiːz kˈæɾɪɡɚɹiz ˌoʊvɚlˈæp tʊ ɐ kənsˈɪdɚɹəbəl dᵻɡɹˈiː.