The Mayo Clinic says,
"Meditation has been practiced for thousands of years. Meditation originally was meant to help deepen understanding of the sacred and mystical forces of life. These days, meditation is commonly used for relaxation and stress reduction."

The Meaning and Purpose of Meditation - at CalmAwareness.com says,
"In its purest definition, meditation refers to the way, the method, path or process by which one is led from within, to a universal center of calm awareness and inspired intuition."

Types:
Religious:
Buddhist Meditation at AccessToInsight.org says,
"Mystics of every religion have induced on themselves states wherein they see visions and hear voices that are in accordance with their own religious beliefs. A Hindu may see images of Hindu Avatars and a Christian may see visions of Jesus.

In Hinduism the reciting of slokas and mantras is employed to tranquilize the mind to a state of receptivity.
Transcendental Meditation (TM) was popularized by Maharishi Mahesh Yogi.

There is an essential difference, then, between Buddhist meditation and concentration and that practiced in other systems. The purpose of Buddhist meditation, is to liberate ourselves from delusion ( false interpretation [vipallasa] on all the sensory experiences we gain through the six channels of cognition) and thereby put an end to both ignorance and craving."

Richard Foster defines it as a spiritual discipline in Christianity where it prepares you for the transforming work of the Spirit, by filling the mind with thoughts on scripture, creation or quiet prayerful discussions with the Lord. See meditation in Christianity.

Stress Reduction:
The Mindfulness-based Stress Reduction or MBSR is a set of Guided instruction in mindfulness meditation practices founded by Dr. Jon Kabat-Zinn at the U. Mass Medical School in 1979. It is designed to reduce psychological stress, anxiety, fatigue and improve mental and physical health.
It is designed to help you focus on the present, not to get somewhere else, but to be where and as we actually are in this very moment. It improves concentration by practicing bringing your attention to one object, such as your breathing.
See more on mindfulness

How to Reduce Stress: 10 Relaxation Techniques To Reduce Stress On-the-Spot at WebMD says,
"If you're thinking meditation means twisting your body into an uncomfortable position and uttering "oohs" and "omms" for an hour, guess again. Any repetitive action can be a source of meditation, says Herbert Benson, MD, author of The Relaxation Response and director emeritus of Benson-Henry Institute for Mind Body Medicine in Chestnut Hill, Mass. This includes walking, swimming, painting, knitting, mowing your lawn -- any activity that helps keep your attention calmly in the present moment.

When you catch yourself thinking about your job, your relationship or your lifelong to-do list, experts say to simply let the thought escape, and bring your mind back the repetition of the activity. Try it for just 5 to 10 minutes a day and watch stress levels drop."

The Tibetan word for meditation "Gom" means "to become familiar with one's Self" and has the strong implication of training the mind to be familiar with states that are beneficial: concentration, compassion, correct understanding, patience, humility, perseverance, etc
See: What is Meditation? at A View on Buddhism.

• Guided meditation. Sometimes called guided imagery or visualization, with this method of meditation you form mental images of places or situations you find relaxing. You try to use as many senses as possible, such as smells, sights, sounds and textures. You may be led through this process by a guide or teacher.
  See Health Journeys - Relieve Stress with guided imagery Kaiser Permanente podcasts.
• Mantra meditation. In this type of meditation, you silently repeat a calming word, thought or phrase to prevent distracting thoughts.
• Mindfulness meditation. This type of meditation is based on being mindful, or having an increased awareness and acceptance of living in the present moment. You broaden your conscious awareness. You focus on what you experience during meditation, such as the flow of your breath. You can observe your thoughts and emotions but let them pass without judgment.
• Transcendental meditation. You use a mantra, such as a word, sound or phrase repeatedly silently, to narrow your conscious awareness and eliminate all thoughts from your mind. You focus exclusively on your mantra to achieve a state of perfect stillness and consciousness.
• Qi gong. This practice generally combines meditation, relaxation, physical movement and breathing exercises to restore and maintain balance. Qi gong (CHEE-gung) is part of traditional Chinese medicine.
• Tai chi. This is a form of gentle Chinese martial arts. In tai chi (TIE-chee), you perform a self-paced series of postures or movements in a slow, graceful manner while practicing deep breathing.
• Yoga. You perform a series of postures and controlled breathing exercises to promote a more flexible body and a calm mind. As you move through poses that require balance and concentration, you're encouraged to focus less on your busy day and more on the moment.
• Relaxation Techniques for Stress Relief: Finding the Relaxation Exercises that Work for You at HelpGuide.org
  These included things like Breathing meditation, Progress muscle relaxation, Body scan meditation, Mindfulness, and Visualization.
  
• Chakra Meditation. You can use hand positions and chants to send energy to the seven chakras (parts of the body).
  See Opening the Chakras
• Mantras:
  Buddhist Mani Mantra "Om Mani Padme Hum"
  Maranatha Mantra, an ancient mantra of Christian tradition. "Ma-Ra-Na-Tha" ("Come Lord" in Aramaic)
  My own "Spirit-Peace-Wisdom-Strength"

Preparing to Meditate:

1. Time
   1. Will become a way of life, but setting aside specific times (especially at the beginning) is critical.
2. Place
   1. Find a place that is free from interruption.
      1. No telephone
      2. Place that looks out on a lovely landscape, if possible
      3. Consistent spot versus looking around each time
3. Posture
   1. It's a myth that you need to be able to get into lotus position in order to meditate effectively. There are other ways to sit, including kneeling, and in fact you can meditate while sitting in a chair or while using a meditation bench.
   2. Comfortable and least distracting (sitting with back straight and feet on the floor, as one example)
   3. Some meditate while lying down, but you are in danger of falling asleep.
      The best position for lying down to meditate is the Alexander Semi-Supine position, where your knees are bent and pointing to the ceiling.
      Oddly, very few people seem to try meditating lying on their side, even though images of the Buddha doing this are abundant.
   4. With a partner. i. Back to back sitting supporting each other. ii. back to back lying down. ii. Sitting facing each other or side by side.
   5. Some times it is helpful to close the eyes to remove distractions
   6. Some times it is helpful to look out at some lovery trees and plants.
   See Meditation posture | Wildmind Buddhist Meditation
4. Time
   
   1. Most say to start with 5 minutes, but some say longer.
   2. 10-15 minutes is common for most.
   3. "How Long to Meditate & How Often to Meditate" at the-guided-meditation-site says to do two 20 minute sessions per day.
5. Aids:
   
   1. Music - The idea that you should listen to music while meditating is very common. But this probably goes back to seeing meditation as little more than a means of relaxation. Some say it is OK.
      

      Traditionally, the idea of listening to music while meditating would be completely out of the question.
      Guided Imagery (see below) may include playing the voice of a guide over music.

      Don't depend on CD's or external sounds according to, Ananda Sangha and Yuttadhammo (Ask A Monk)
      

   2. Incense, Aromatherapy. - It is believed that incense carries our prayers and wishes to the heavens. Watching trails of smoke curl and waft upwards can be relaxing.
      Some think that aromatherapy can alter brain waves and behavior.
      See Aromatherapy for Stress - Aromatherapy Research and Techniques
   3. Candles - The flame of a candle has long been associated with the flame of spirit that resides within.
      For some people this type of meditation is quite easy, as they find it easier to let go of thoughts when they are concentrating on a physical "thing" rather than on a mantra.
      See How to Use Candles in Meditation | eHow.com.
   4. Guided Imagery - Guided imagery may include playing the soft voice of a person over a musical background guiding you through a series of relaxing visualizations.
      See Guided Imagery - The Power to Heal, Transform and Relax! at the-guided-meditation-site.com
      See Health Journeys - Relieve Stress with guided imagery Kaiser Permanente podcasts.

• Observe how it feels
• Notice what's going on around you.
• Listen to the sounds around you
• Feel - Notice any sensations or feelings
• Come back to the rhythm of your walk when your mind wanders off

Difficulty in emptying your mind:
"How to Meditate Without Even Trying", by physicist Peter Russell has some tips. A short summary of his Huffington Post Article:

"When I first became interested in meditation, back in the mid-60s, I was repeatedly told that it took great mental discipline and many years of practice. And my experience appeared to confirm it. My mind was full of thoughts, and try as I may, I could not keep them at bay. Like many others, I naturally assumed that I was not trying hard enough; I needed greater mental discipline, not less."

Then I chanced upon Transcendental Meditation. Its teacher, the Maharishi of Beatles fame, challenged the whole notion of trying to control the mind.

We are so busy worrying whether or not we are going to be at peace in the future, we don't give ourselves the chance to be at peace in the present.
...
Thus the advice that occurs repeatedly in a variety of meditation traditions is:

1. When you realize you have been caught in a thought, accept the fact. Don't judge or blame yourself. It happens, even to the most experienced meditators.
2. Instead of following the thought, as you might in normal life, gently shift your attention back to some experience in the present moment. In TM that may be the thought of a mantra, in mindfullness the sensation of the breath, or in other practices perhaps a visual image, or a feeling of love.
3. Let the attention rest in that experience. Don't try to concentrate or hold it there. Ah yes, you will be sure to wander off again. But the practice is not so much learning how to stay present, but how to return to the present. If you wander off a hundred times, that is a hundred opportunities to practice gently returning your attention to the present.

Huffington Post Article Author's web site "How to meditate without even trying" http://www.peterrussell.com/

Books:
Buddhist Boot Camp by: Timber Hawkeye

Links:
Mindfulness
About Meditation - The Meaning and Purpose of Meditation - Meditate for Calm Awareness
Meditation: Take a stress-reduction break wherever you are - MayoClinic.com
Relaxation Techniques for Stress Relief: Finding the Relaxation Exercises that Work for You at HelpGuide.org
Meditation | Mindfulness | Guided Meditation | Stress Management | Andy Puddicombe | Headspace
How to Reduce Stress: 10 Relaxation Techniques To Reduce Stress On-the-Spot at WebMD
Health Journeys - Relieve Stress with guided imagery Kaiser Permanente podcasts.
Huffington Post: Kripalu Center for Yoga and Health - Meditation for Beginners
Peter Russell: How to Meditate Without Even Trying
A variety of stress reduction techniques at The Human Brain - Relieve Stress at the Franklin Institute.
Meditation Aids / Tools
Meditation aids and products
Relaxation Techniques for Stress Relief: Finding the Relaxation Exercises that Work for You
Even More Meditation Aids for the iPhone, iPod, iPad and More | Metta Refuge
Meditation In Action: Turn Your Walk Into A Mindful Moment at Huffington Post
Mantras | The Buddha Center

Links:
Spirituality, Mindfulness, Personal Growth... resources under Religion

Return to Mental health or Alternative Medicine.

Fresh Air - How Meditation Can Ease Pandemic Anxiety - Dan Harris on Fresh Air