Over the last 2000 years, traditional variations have emerged among the traditional liturgical customs of different Jewish communities, such as Ashkenazic, Sephardic, Yemenite, Eretz Yisrael and others, or rather recent liturgical inventions such as Hassidic, and Chabad. However the differences are minor compared with the commonalities. Most of the Jewish liturgy is sung or chanted with traditional melodies or trope. Synagogues may designate or employ a professional or lay "hazzan" (cantor) for the purpose of leading the congregation in prayer, especially on Shabbat or holidays.