It is a continuous scale of time, without leap seconds, and it is the principal realisation of Terrestrial Time (with a fixed offset of epoch).
ɪɾ ɪz ɐ kəntˈɪnjuːəs skˈeɪl ʌv tˈaɪm, wɪðˌaʊt lˈiːp sˈɛkəndz, ænd ɪɾ ɪz ðə pɹˈɪnsɪpəl ɹˌiːələzˈeɪʃən ʌv tɚɹˈɛstɹɪəl tˈaɪm wɪð ɐ fˈɪkst ˈɔfsɛt ʌv ˈɛpɑːk.