What does Big Blind Special mean in poker?

Big Blind Special is a situation where the player in the big blind wins the pot or makes a strong hand with cards they probably would not have played from another position. This usually happens because they got to see the flop for little or no extra cost.

What does it look like in practice?

For example, several players limp into the pot, and the big blind checks and stays in the hand with a very weak holding. Then, on the flop or later streets, that hand unexpectedly improves and wins a solid pot. That kind of scenario is what players call a Big Blind Special. The term is informal, but poker players understand it quickly: it refers to an unexpected piece of value or luck from a position where the player was already in the pot because of the forced blind.