Meditation is the practice of watching your mind think. Why would you want to watch your mind think? Well, when you can watch something, you will come to know that you are not that something. You cannot watch and be what you are watching at the same time. The Sanskrit term for this watcher or witness is sakshi.
A yogi strives to shift his or her mis-identification with body and mind to identification with the indwelling Divine Self, whose nature is eternal happiness.
All yoga practices, including meditation, are designed to allow happiness to radiate through every cell and tissue of the body and every vibration of the mind. Through these practices, the yogi seeks to clear the mind of all thoughts that cloud the truth of the psyche, (which is the inner soul, or Self), that it exists eternally in a state of happiness. To truly be happy we must bring the mind into a condition of clear perception. With clear perception the mind reflects the Self, like a clean mirror.
In the first chapter of the Yoga Sutras, Patanjali answers the question: What is Yoga with a description of the result gained through the practice of deep mediation:
Yogash chitta-vritti-nirodhah. (YS I:2)
Yoga is the cessation of the fluctuations, or whirlings of the mind.
When you stop identifying with your thoughts, the fluctuations of mind, then there is Yoga, which is identification with the true Self; samadhi, happiness, bliss and ecstasy. The Sanskrit term for meditation is dhyana.
Just as you cannot ‘do’ Yoga you cannot ‘do’ meditation. The experience of mediation is graceful, it cannot be attained by effort. But grace arises only after the mind has been purified through much effort. Through consistent mediation practice one becomes able to sit still long enough to be able to concentrate the mind so that it becomes balanced, steady and one pointed. When this concentration is intense enough and long enough then concentration will become mediation. If meditation is intense enough and long enough then it will move into a state bliss or samadhi.
Excerpt from Chapter 10, Jivamukti Yoga by Sharon Gannon & David Life.