During the Shabbat Torah service, seven men are called by the Gabbai (Torah service coordinator), to "come up" to the Torah for an aliyah (honor). There is one aliyah for each portion of the Torah that is chanted. An additional aliyah, designated the Maftir aliyah, is given to the person who will read the Haftorah. The Haftorah is a chapter of Prophets that is designed to express poetically and prophetically the messages included in the Torah reading for the day.
The first aliyah is given to an individual who is a descendant of Kohanim (the priestly families who served in the time of The Temple). The second aliyah is given to an individual who is from the tribe of Levi. The remaining aliyot are given to descendants of the other Israelite tribes ("Yisroel"). If no Kohen is present, a Levi or Yisroel may be called for the first aliyah.