Digitial signal processing?
From what I can remember from school, DSP takes a real-world signal, like a sound input, and mathematically alters it to improve the sound. For instance, when you talk on a phone DSP takes in your voice, and removes the background noise allowing the person you are speaking to to hear crystal-clear responses from you.
If you plan on doing any recording, music making, or game playing on your pc with a surround sound system on it, then its is VERY important. You want the best sound quality you can get.