The most well-known name for the holiday is Sukkot, or “booths:”
דַּבֵּר אֶל־בְּנֵי יִשְׂרָאֵל לֵאמֹר בַּחֲמִשָּׁה עָשָׂר יוֹם לַחֹדֶשׁ הַשְּׁבִיעִי הַזֶּה חַג הַסֻּכּוֹת שִׁבְעַת יָמִים לַה’׃
Speak to the Children of Israel saying, on the fifteenth of this seventh month shall be a festival of booths (Sukkot) to the Lord, for seven days. (Vayikra 23:34)
We are told that the holiday of Sukkot falls on the 15th of the seventh month, which is Tishrei. It is interesting to note that while we consider Rosh Hashanah the start of the new Jewish year, the Torah counts the months starting with Nissan, thus Tishrei would be the seventh month.
What is the significance of sitting or even living in a sukkah? In the same way that our ancestors dwelled in temporary booths or sukkot after the Exodus from Egypt, we do the same to connect to the chain of tradition:
בַּסֻּכֹּת תֵּשְׁבוּ שִׁבְעַת יָמִים כָּל־הָאֶזְרָח בְּיִשְׂרָאֵל יֵשְׁבוּ בַּסֻּכֹּת׃ לְמַעַן יֵדְעוּ דֹרֹתֵיכֶם כִּי בַסֻּכּוֹת הוֹשַׁבְתִּי אֶת־בְּנֵי יִשְׂרָאֵל בְּהוֹצִיאִי אוֹתָם מֵאֶרֶץ מִצְרָיִם אֲנִי ה’ אֱלֹקיכֶם׃
For seven days you shall live in booths (Sukkot); all citizens of Israel shall live in booths, in order that future generations may know that I made the Children of Israel live in booths when I brought them out of the Land of Egypt, I am the Lord your G-d. (Vayikra 23: 42-43)
Sukkot is also the time we start to pray for rain. It is an opportunity to consider the natural environment by being more immersed in it, as well as traditionally showing faith in G-d by leaving ourselves more open to the elements. Another environmental element of the chag is the holding and waving of the Arbat Haminim (ארבעת המינים), Four Species of Sukkot’s ritual plants—lulav, etrog, hadassim (myrtle leaves), and aravot (willow leaves). In addition, the name Sukkot is also a reminder of the value of hospitality, as we traditionally invite in the Ushpizin (“guests” in Aramaic)—different Biblical leaders on each night of Sukkot.