Sukkot, the Feast of Tabernacles or Booths, begins on the 15th day of the seventh Scriptural month, and is a seven day long moed/appointed time. The first day is a day of rest, and there were sacrifices ordained for each of the seven days. Every seven years, the Torah was to be read publicly to the people, and it was to be a time of great rejoicing (actually commanded, Deut 16:14) because of the blessings and increase that YHWH had given His people. By this time of year, all the produce of the land would have been harvested and stored, so it was a real time of thanksgiving. (Interestingly, there is some evidence to suggest that the original Thanksgiving that the pilgrims had in America was a Sukkot celebration.)