The weekly biblical reading often chanted by a bar or bat mitzvah celebrant after the Torah reading is called the haftarah.
The haftarah is a selected passage from the books of the Hebrew Bible, especially the Prophets. It is read or chanted after the weekly Torah portion in many Jewish synagogue services. The passage is usually connected thematically to the Torah reading or to the calendar.
A bar or bat mitzvah student often spends months learning the melodies and pronunciation needed to chant the assigned haftarah. The student may also deliver a speech explaining the Torah portion, haftarah, or a related ethical idea. Local customs determine how much of the reading the celebrant performs.
Haftarah is not another name for the Torah. The Torah consists of the Five Books of Moses, while the haftarah comes from later biblical books. The term is also unrelated to Haggadah, the text used during the Passover seder.