Meditation is knowing oneself through the experience of bliss of oneness. The systematic steps of Yoga withdraw the mind from the external senses and make it concentrate inward. This internal focus harmonizes the mind with cosmic consciousness. Any activity where personal identity is lost as it merges into nothingness is an example of meditation.
The confined drop of a cramped self-centered personality is lost when it merges into the open ocean of infinite consciousness. This tranquil awareness puts a person into a state of restful alertness which relaxes the mind & body beyond the realm of sleep. This restful awareness is exemplified by Lord Vishnu who maintains the entire creation but remains always relaxed with eyes closed on a great serpent with many heads.