In essence, meditation allows the awareness to become 'rejuvenated'. Meditation can be considered a technique, or practice. It usually involves concentrating on an object, such as a flower, a candle, a sound or word, or the breath. Over time, the number of random thoughts occuring diminishes. More importantly, your attachment to these thoughts, and your identification with them, progressively become less.
Meditation can also be objectless, for example consisting of just sitting.
Experiences during meditation probably vary significantly from one individual to another, or at least if different techniques are involved. Relaxation, increased awareness, mental focus and clarity, and a sense of peace are the most common biproducts of meditation. While much has been written about the benefits of meditation, the best attitude is not to have any expectations when practicing. As well, since meditation involves becoming more aware and more sensitive to what is within you, facing unpleasant parts of oneself may well be part of meditation. Regardless of the experience, the meditator should try to be aware of the experience and of any attachment to it.