every networkable device
every networkable device has a MAC address. If you are talking about a computer, you can either look on the back, bottom and check it out, or go to START, RUN, type in CMD, hit enter, then type in IPCONFIG, and it will list the network adaptors that are there, and their respective MAC addresses.
If you have a laptop, it will most likely have an ethernet port (networkable) and a MAC address, AND a WIFI card of some sort, with ANOTHER MAC address.
Your replay DVR will have one, homeplug jacks have them, PDA's have them, etc. Someday, I think they are going to run out, or have to use newer networking standards to expand the pool.
most cell phones will have them in the future, watches, tvs, dvd players, everything that is either now, or in the future networkable needs it.
btw, MAC stands for MEDIA ACCESS CONTROL and they are assigned by vendor. So, for hackers it is nice to know which vendor the MAC address is coming from, makes hacking into a machine easier since the list of know vulnerabilities get a bit narrowed.
:-) but who would ever do that!