Rabbi of a congregation - Jewish scholar who is charged with answering the legal questions of a congregation. This role requires ordination by the congregation's preferred authority. A congregation does not necessarily require a rabbi. Some congregations have a rabbi but also allow members of the congregation to act as shatz or baal kriyah.
Hassidic Rebbe - rabbi who is the head of a Hasidic dynasty.
Hazzan - a trained vocalist who acts as shatz. Chosen for a good voice, knowledge of traditional tunes, understanding of the meaning of the prayers and sincerity in reciting them. A congregation does not need to have a dedicated hazzan.
Shaliach tzibur or Shatz leads those assembled in prayer, and sometimes prays on behalf of the community. When a shatz recites a prayer on behalf of the congregation, he is not acting as an intermediary but rather as a facilitator. Any adult capable of reciting the prayers clearly may act as shatz.
The Baal kriyah or baal koreh reads the weekly Torah portion. The requirements for being the baal kriyah are the same as those for the shatz.
Gabbai (sexton) - Calls people up to the Torah, appoints the shatz for each prayer session if there is no standard shatz, and makes certain that the synagogue is kept clean and supplied.
