Paul has given you a good definition of what it is. Some advantages are that it stablilizes woods like burls and such, making many of them usable for forearms and such when cored. It also allows color enhancement that looks better than normal dying as the dye goes all the way through the piece. A disadvantage is that it makes the wood really heavy. So coring is just about a must on these. Another advantage in some applications is you do not have to use a finish on it as you can sand the wood to a real fine grade sand paper and buff it out. That only works well with the fine grain types, or the veneered types like Dymondwood. Not having to put a finish on is great for pens and knife handles and some cues, although it is more limited in cues.