The word pit has several meanings:

1. A large hole in the ground. Workers might dig a pit to lay a building's foundation, or archaeologists might excavate a pit to search for ancient artifacts. A snake pit is a hole where venomous snakes gather. Coal miners once worked deep in mining pits, extracting coal from underground. The phrase the pits means something is terrible or the worst possible, like saying, “That rainy campout was the pits!”
2. The hard seed inside certain fruits. A peach pit, cherry pit, or olive pit is the tough center you can't eat. Some people call these stones instead. If you're making cherry pie, you need to remove all the pits first.
3. To set in competition against someone. If your teacher pits you against your best friend in a spelling bee, she's matching you as opponents. The phrase pitted against often describes facing a difficult challenge: “The small team was pitted against last year's champions.”
4. Small dents or hollow marks on a surface. Hailstones can pit a car's hood, leaving dozens of tiny dents. Rust can pit metal over time, creating rough spots where the surface was once smooth.