For my friend that don't know what boxing mean in this context, it basically mean that you are playing more than 1 account in the same game at the same time. Try to imagine you controlling 2 wow character at the same time. I never tried it, but I know for sure it is difficult for me.
Usually in the mmo community, it is common to see people box 2 character, while some go to 4. But for this guy he go way beyond and box 36 shaman at one time!!! I don't know how he did it, or agree on his point, but it does sure that when you really compassion on your hobbies, you can go beyond the norm.
There is another one go to 50!!!
You can read more on www.dual-boxing.com