Im a newb too but i will try and explain it to my best knowledge! Topping is when you cut off the "top" of your plant after a new growth has occurred! Most people do this because it creates two new shoots (sometimes four or even more like PBF said, but most of the time this is done by fimming) for more colas to be formed. I have read a lot about topping compared to not and some people say that not topping gives you about the same amount of yield but stronger bud! Others disagree but i think its all preference! Look around on this site about topping and you will find everything you need to know about it....there are some really awesome threads on it! I could go on and on about the details but i would just check out a thread!! hope this helped a little man!!!