Meditation is a part of the class skills set of a Mage and Hunter. The skill helps you to regenerate mana.

Skill’s efficiency

The skill can be used only when standing still.
The amount of restored mana depends on the character’s level and Meditation efficiency.

Ways of leveling your Meditation

The delay between the next use of the skill is 10 seconds. Meditation will additionally train on its own while you are training other skills.
One of the most effective ways to train your skill is to put on clothes, meditate and remove the clothes.
One of the simplest ways is to use other skill that requires mana and to restore it with Meditation.

Here is a detailed video of how the skill is used: