What is the holiday which commemorates the final plauge that god sent to encourage the pharaoh to release the Jews called and what is a special meal that is held called?

Answer 1

You're obviously referring to the holiday of Pesach (Passover). However, Pesach does not commemorate one specific plague, it commemorates the whole story of the exodus.

The first night in Israel and first two nights outside of Israel are observed by a religious ceremony held in the home. The ceremony is called a seder which is held around a meal. The word seder means 'order'.