👉 Covariance is a measure of how two or more variables change together. It's like measuring how much one variable changes based on how another variable changes. For example, if you have two different types of apples and their prices are inversely proportional to each other (meaning they go up in price when the price of one goes down), then you can calculate the covariance between the prices of apples. Covariance is a useful tool for understanding how much two variables change together over time or space.