A long time a go in syracuse ancient greece there was a great mathematician named Archimedes. One day when he was taking a bath he discovered something life changing. When he got in some water got displaced and it over float over the bath tub.
Archimedes discovery got him thinking. He was so excited that he ran through the streets without any cloth on shouting eureka ! eureka ! this meant I have found it in greek.
He figure out that if you put something in water and it is lighter then the amount of water being displaced, the object will float. This is known as buoyancy or the Archimedes principle. So if the object can float it is buoyant.