Paarthurnax is an ancient dragon who resides at the Throat of the World, the very peak of High Hrothgar, and acts as the leader of the Greybeards. He is a dragon who has been in hiding for thousands of mortal years, waiting for Alduin to return.
In the first conversation with him, he tells you about meditation: Fus, Feim, and Yol. You can choose one of them (although, you can return and change your selection whenever and as often as you want), and will get a bonus from that:
Fus (Effortless Power): The probability that you will be pushed back by enemy attacks falls by 25%, while your attacks cause 25% more on the opponents.
Feim (Eternal Spirit): In ethereal form your health regenerates 25% faster.
Yol (The Inner Fire): Fire-Breathing shout causes 25% more damage.