The phrase "Iron sharpens Iron" is a proverb that means two things can help each other to improve. It refers to how one person or thing can be improved by another, through their interactions and mutual influence on each other. This saying comes from the Bible in the book of Proverbs 27:17 which states "Iron sharpens iron; so a friend sharpens a friend." The phrase is often used metaphorically to describe how people can learn from one another, or how different experiences and perspectives can help us grow.