Meditation is usually thought of as the act of calming and focusing the mind in one-pointed collectedness. This discipline includes avoiding thought processes and random fantasies. Another view of meditation is that it isn't so much an act as something that just happens. Different practices involve focusing one's attention differently, and a variety of positions and postures including sitting cross-legged, standing, laying down, and walking (sometimes along designated floor patterns).
Contemporary proponents of meditation make various claims that it can lead to reductions in stress, hostility and illusions & attachments, and can be helpful in treating mental illness. On the other hand there is evidence that meditation can lead to more mental problems in psychiatric patients. Traditionally, meditation has been seen as a means of gaining experiential insight into the nature of reality (religious/spiritual or not), or communing with the Deity/Ultimate Reality.
In the samadhi or shamatha, or concentrative, techniques of meditation, the mind is kept closely focused on a particular word, image, sound, person, or idea. This form of meditation is found in Buddhist and Hindu traditions including Yoga, in Medieval Christianity, Jewish Kabbalah, and in some modern metaphysical schools. Related to this method is the method developed by Eknath Easwaran. He called it "passage meditation" ? silent repetition in the mind of memorized inspirational passages from the world?s great religions. As Easwaran says, "The slow, sustained concentration on these passages drives them deep into our minds; and whatever we drive deep into consciousness, that we become."
In Vipassana (insight, or seeing things as they are) meditation the mind is trained to notice each perception or thought that passes, but without "stopping" on any one. This is a characteristic form of meditation in Buddhism, especially in some Theravada traditions, and is also a component of zazen, the term for meditation practice in Zen. In at least some forms of vipassana, you do not attend to whatever perceptions arise, but purposely move your attention over your body part by part, checking for perceptions, being aware and equanimous with them, and moving on. This form of meditation has some resemblance with the kind of meditation that Jiddu Krishnamurti talked about.
In annapuna meditation attention is focused on the breath.
Transcendental Meditation requires no concentration or focus.
See also: Qi, Qigong,