A z1g is very similar to a n00b. It is a more harsh way to make fun of a n00b. If a n00b becomes excessivly n00bish they become a z1g. To "take off" a z1g is to kill, destory, defeat, or demoralize them in some way.
An even harsher word to call a z1g by is z1ggy n00b.