Fatliter goes by many different names. Pineheart, fat wood, or heart of pine are some of them. Whatever you call it, it makes for a great fire starter. I burn a lot of wood during the winter time. Mostly hickory, oak, and lately chestnut. I can't imagine starting a fire without it.
Basically fatliter is the very center of a pine tree. Over time the sap in a pine tree hardens into a rock hard substance that is very resinous. The fatliter never rots. Often times it is the only thing left from a pine tree. It will get a fire going really hot. It will burn even when wet. If you break a piece in half it will smell piney. It's just great stuff that is indispensable.