This is the area between a woman's anus and vagina. Previously referred to as the "taint". Land-bridge gives women their own word for this area. The phrase was created because the area is between two holes, like two oceans. The land-bridge connects the vagina to her ass. And it's a lot more fun to say than "taint".
I was fingering her, then my fingers crossed the land-bridge and played with her ass.