Leaven is a food ingredient that causes dough to rise via fermentation. Yeast is a common leavening ingredient.
See the entry for yeast for more information about the symbolic meaning of leaven and yeast, us well as unleavened.
Key verse about Leaven: Burn leavened bread as a thank offering and brag about your freewill offerings— boast about them, you Israelites, for this is what you love to do,” declares the Sovereign Lord (Amos 4:5, NIV).
A lifelong student of the Bible, Peter DeHaan, PhD, wrote the 1,000-page website ABibleADay.com to encourage people to explore the Bible. His main blog and many books urge Christians to push past the status quo and reconsider how they practice their faith in every area of their lives.