What does it mean if an egg floats in water and how can this be used to determine its freshness?

If an egg floats in water, it means that it is not fresh. This is because as eggs age, air enters the egg through the porous shell, causing it to become less dense and float. Fresh eggs sink to the bottom of the water because they have less air inside. This simple test can be used to determine the freshness of an egg before cracking it open.