Pocket Springs
Pocket Springs are springs that are individually encased in a pouch of material, and offers less motion transference than open coil springs.
The amount of individual springs in a mattress will determine if the mattress is a medium, or firm support. 1000 pocket springs is a medium support, 1500 springs firm support and 2000 is the firmest support.
Very high spring count mattresses are usually in the top end of the range and also use micro springs for extra comfort and durability