Sound Proofing refers to creating the perfect studio space, acoustically, by eliminating factors in your recording space that will negatively affect the result such as natural reverb and standing sound waves. By using various styles of acoustic foam and acoustic foam panels, you are able to take control of these factors.
Egg crate and wave shaped sound foam pieces will absorb mid/high frequencies to prevent them from bouncing back off your walls and other surfaces. Bass traps will slow the movement of low frequencies out of the corners of your room and isolation pads will remove environmental factors in the reproduction of sound out of your monitors by making them behave as if they are floating in the air and not in contact with your desk.
Sound proofing by using one or a combination of the above products, will allow your studio to be fully optimised to achieve high quality sound.