A split pot is a pot that is shared by two or more players on a showdown. This only happens when there are more than one player with the same best hand.
For example, the board runs K-Q-3-3-7. The first player shows down K-J, and the other player turns over K-9. In this instance, both players have the same five-card hand – two pairs (Kings and Treys) with a Queen kicker.
Since they both have the same hand, they each win half the pot, i.e., it is a split pot. Another term you’ll come across to describe this exact situation is a chopped pot.