A Spring Mattress Set consists of 2 parts. The mattress and the box spring.
The mattress is the top part, which is slept on. The bottom part is the box spring which is made of a wooden frame covered in fabric that acts as a foundation for the mattress. Box springs act as a shock absorber for the mattress and can help prolong the life of the mattress. It is also used to elevate the height of the mattress instead of placing the mattress on the floor.
You can purchase it as a set or you can use a bed frame instead of a box spring.