A pig bladder is an organ that comes from a pig's body. It's a special part of the pig that can hold pee (pee-pee) and other waste (poo-poo).
Sometimes, after a pig is killed for food, people can take out the bladder and clean it really well. Then, they use it to make things like soccer balls or medicine capsules.
When the bladder is used to make a soccer ball, the people put air inside the bladder and sew it up tight. Then, they cover the bladder with a special kind of material that makes it easy to kick and play with. So, when you play soccer with a ball made from a pig bladder, you're actually playing with a part of a pig!
But don't worry, even though a pig bladder may sound strange, it's just another part of the pig's body that people can use for useful things.