If the data set is a statistical sample (a subset of the population), it is called the sample mean (which for a data set  is denoted as ).
ɪf ðə dˈeɪɾə sˈɛt ɪz ɐ stɐtˈɪstɪkəl sˈæmpəl ɐ sˈʌbsɛt ʌvðə pˌɑːpjʊlˈeɪʃən, ɪɾ ɪz kˈɔːld ðə sˈæmpəl mˈiːn wˌɪtʃ fɚɹə dˈeɪɾə sˈɛt ɪz dᵻnˈoʊɾᵻd æz.