A Four of a Kind is a hand where four cards have the same rank.
The rank of the four of a kind cards determines the relative
ranking amongst different four of a kind hands. The higher the
rank of the four of a kind cards, the higher the rank of the hand.
This means Four of a Kind, Aces is the best possible hand of
this type, and Four of a Kind, Twos is the lowest possible
hand of this type.
Example:
versus
Player 1 has Four of a Kind, Aces:
Player 2 has Four of a Kind, Eights:
Player 1's Quad Aces beats Player 2's Quad Eights.