A long time ago in Syracuse, Ancient Greece there was a great mathematician name Archimedes. One day when he was taking a bath he discovered something life changing. When he got in some water got displaced and it overflowed over the bath tub.
Archimedes discovery got him thinking. He was so excited that he ran through the streets without any clothes on shouting Eureka ! Eureka ! This meant that I have found it in greek.
He figure out if you put something in water and it is lighter than the among 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.