What is known about the Feast of Unleavened Bread?

Ezra 6:22 (ESV)

22 And they kept the Feast of Unleavened Bread seven days with joy, for the LORD had made them joyful and had turned the heart of the king of Assyria to them, so that he aided them in the work of the house of God, the God of Israel.

This feast began on the day following Passover and lasted seven days in total (Leviticus 23:6–8). During this week, the Jews were forbidden from eating leavened bread. (The difference between leaven and unleavened bread is found in the word itself: leaven. Leaven is what is placed in bread dough to make the bread rise. No yeast is used (Deuteronomy 16:3).) The first and seventh days were to be days of rest (Exodus 12:16. This festival commemorated the hasty departure of the Jews from Egypt.