Your mattress is the padded part of your bed that rests on top of the frame or box springs and is covered in a sheet. Some people prefer a soft, squishy mattress, while others like their mattresses firm.
Some mattresses have a system of springs inside to provide just the right amount of firmness and bounce when you lie on them. Others are made of a dense kind of foam that supports a sleeper's body comfortably. The earliest mattresses were filled with straw or horse hair, and in many societies people don't sleep on mattresses at all, instead using mats or futons. The Arabic root of mattress is al-matrah, "thing thrown down."