Gish Gallop is a debate technique where someone tries to overwhelm their opponent with a lot of complicated information. It's named after a debater named Duane Gish who often used the technique in the 1970s.
In a Gish Gallop, the person using it tries to throw out as many points as possible, often without worrying about how accurate they are. It's a way to try to confuse their opponent and make them think they don't know as much as they do.