MAC Address: the Media Access Control address is a hard-coded or physical address present on anything that accesses the Internet. Your wireless router has one, your UMA capable handset has one, the backbone router your ISP uses probably has many, etc. It consists of a 48-byte address in the format nn:nn:nn:nn:nn:nn using the hexadecimal number system. Everything you ever wanted to know about a MAC address: MAC Addresses
MAC Filtering: A way to allow or deny certain devices from connecting to a wireless router based on the MAC address of that device. For example, if I only want my laptop to be able to connect to my wireless router I would set my router configuration to allow the MAC address of my laptop but deny all others. More information on MAC filtering: MAC filtering
QoS: Quality of Service is a method of placing priority on certain types of packets, a certain network service, or even a certain device. This is very important when it comes to making calls over an Internet connection since you *need* the voice packets to go out first over data packets (i.e., someone surfing the 'net, downloading a file, etc.). With no QoS if you are chatting over your UMA handset and someone starts a download the voice quality of your call may suddenly go from great to horrible and finally your call may just drop. A website with a much more in-depth description: QoS
Category-5 or cat-5: A term used to describe the standard 8-wire Internet cable used in many places today. Your computer (non-wireless) is using a cat-5 cable to plug into your router. The cable modem is using a cat-5 cable to plug into your router, etc. A website with more information: Category-5
Someone correct me if I'm wrong on any of the above. It's late and I'm sleepy.