esoteric

es·o·ter·ic –adjective
1. understood by or meant for only the select few who have special knowledge or interest; recondite: poetry full of esoteric allusions.
2. belonging to the select few.
3. private; secret; confidential.
4. (of a philosophical doctrine or the like) intended to be revealed only to the initiates of a group: the esoteric doctrines of Pythagoras.