What is pillow sex? Help!?

Im 17 next month and i've heard about pillow sex. I don't know what it means, and it sounds daft cos how can you have sex with a pillow. People help me cos i don't even know what it means. Does it feel nice or horrible. What do you do! I don't know, someone give me ideas or a website that i could visit. NO HORRIBLE ANSWERS PLEASE! Thank you!