Unleavened bread (Bread without yeast) refers to bread baked without yeast. Because it lacks yeast, it actually resembles a hard cracker.
During the Exodus, it strongly carried the meaning of food quickly baked and eaten when there was not enough time to ferment bread due to the hasty departure.
Exodus 12:34So the people took their dough before it was leavened, their kneading bowls being bound up in their clothes on their shoulders.
It was also called the bread of affliction.
Deuteronomy 16:3You shall not eat leavened bread with it; seven days you shall eat unleavened bread with it, the bread of affliction, for you came out of the land of Egypt in haste. That you may remember the day when you came out of the land of Egypt all the days of your life.
When King Saul visited the medium and was weak, the woman quickly baked and served unleavened bread when she cooked.
1 Samuel 28:24Now the woman had a fattened calf in the house, and she quickly killed it. And she took flour and kneaded it and baked unleavened bread from it.
Paul used the expression "unleavened bread" to represent the pure state of a Christian.
1 Corinthians 5:6Your boasting is not good. Do you not know that a little leaven leavens the whole lump?1 Corinthians 5:7Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our Passover lamb, has been sacrificed.1 Corinthians 5:8Let us therefore celebrate the festival, not with the old leaven, nor with the leaven of malice and evil, but with the unleavened bread of sincerity and truth.