From BiblePortal Wikipedia

Tabernacles [1]

Feast Of, a solemn festival of the Hebrews, observed after harvest, on the fifteenth day of the month Tisri,  Leviticus 23:34-44 . It was one of the three great solemnities, wherein all the males of the Israelites were obliged to present themselves before the Lord; and it was instituted to commemorate the goodness of God, who protected them in the wilderness, and made them dwell in tents or booths after they came out of Egypt. ( See Feasts. ) This feast continued eight days, of which the first and last days were the most solemn,  Leviticus 23:34 , &c. It was not allowed to do any labour on this feast, and particular sacrifices were offered, which, together with the other ceremonies used in celebrating this festival, were as follows: The first day of the feast they cut down branches of the handsomest trees, with their fruit, branches of palm trees, and such as were fullest of leaves, and boughs of the willow trees that grew upon the sides of brooks,  Nehemiah 8:16 . These they brought together, and waved them toward the four quarters of the world, singing certain songs. These branches were also called hosanna, because when they carried them and waved them, they cried Hosanna; not unlike what the Jews did at our Saviour's entry into Jerusalem,  Matthew 21:8-9 . On the eighth day they performed this ceremony oftener, and with greater solemnity, than upon the other days of the feast. They called this day hosanna rabba, or "the great hosanna."