Shemini Atzeret is the holiday which is celebrated on the eighth day of Succot (Tishri 22).
In Israel, it is celebrated for one day, which is a combination of Shemini Atzeret and Simchat Torah.
In the Diaspora, Shemini Atzeret and Simchat Torah are separated, with Shemini Atzeret being celebrated on the eighth day, and Simchat Torah being on the ninth day.
What is Shemini Atzeret?
When the day of Sukkot comes to an end, seven days after its beginning, Shemini Atzeret & Simkhat Torah begin. Have you ever been on a trip and enjoyed your company so much you extended the trip a day? That’s a prime simile for how God extends the celebration of Sukkah out one day for the Jewish people, in aims of a more intimate relation. The Torah is read throughout the week and at the end of the entire Torah portion a celebration is in order.
Often these two Holidays are considered a part of Sukkot, close in date relation but this is very wrong as they are two different entities.
Chatan Torah and Chatan Bereshit
The other main custom for this day involves the Chatan Torah and Chatan Bereshit, which takes place during the Morning Service (Shacharit) on Simchat Torah.
"Chatanim" is the plural of "Chatan", which means bridegroom.
"Chatan Torah" is the title given to the individual who is called to the Torah with a beautiful chant - describing his greatness in glowing terms - and is given the honour of reciting the blessing over the last section of the Torah to be read in the current year.
The "Chatan Bereshit", "Bridegroom of the (Beginning of the) Torah," also a great honour, is called to the Torah with a similar introduction as that which introduced his fellow Chatan. He is given the honour of reciting the blessing over the beginning of the Torah, the section dealing with the Creation of the Universe by G-d