All your noobish questions shouldn't be addressed in the Android Development Section.
I mean, come on people, if you don't know what the hell is overclocking, than wtf are you even doing here?!?!? It takes two seconds googling to find out, and if you can't even do that...
Leave this section for the developers, not for NOOBS !!!!
It might be a slightly stupid question, but you gave a completely retarded answer. Get off his back, he's mabye new here, and wanted to learn from the pro's. This place is not only about the devices, but also the community, and you aren't helping either.
OT:
Overclocking is when you increase the frequency on your processors clocks. This gives your device more power, since is has more power to work with. OC'ing can also be dangerous for your phone, and CAN eventually kill it, if it isn't clocked properly. If it's unstable, it's not a good sign.
Netfilter are, correct me if I'm wrong here, codes injected into the kernel. These codes makes, ex., tethering possible.
Undervolting is when you decrease the voltage given to the phones hardware, in order to save the life of the battery. This also gives slightly to much less performance.
Hope you understand my explainations