The oversized chip rule in poker is when a player uses a single large denomination chip or multiple large denomination chips to make a bet following a previous bet. If the value of the chip(s) is greater than the previous bet, it is considered a call if the player does not leave enough chips behind to equal the previous bet. If there are enough chips left behind to equal the previous bet, plus 50% or more of the previous bet, then it is considered a raise. This rule helps determine whether a bet is just a call or a raise of the previous bet.