A full house is any poker hand that contains a three-of-a-kind hand and a pair. It is the fourth strongest hand in traditional poker hand rankings, just below a four-of-a-kind and stronger than a flush.
For example, if you are holding AJ and the board comes as AJ52J, you just hit your full house on the river, also known as a boat.
The strongest possible full-house hand includes three aces and two kings and is known as Aces Full of Kings. Oppositely, three twos and two threes is the weakest full-house.