Meditation is a way of clearing the mind by focusing one's attention on a single thing. There are many forms of meditation, such as seated meditation, standing meditation, walking meditation, visualization, and chanting meditations.
Mantra Meditation is a form of meditation that uses the power of words to direct the mind to one single point where the use of a key word, or words, helps the individual to focus on a specific issue, topic, or area of personal growth. The word, or words, can be thought of internally, or chanted externally, depending on the preference of the person meditating.
An example of Mantra Meditation, which was described by Thich Nhat Hanh, is to think or say the word "calm" while inhaling during meditation, and then think or say the word "smile" while exhaling. Another mantra that can be used while doing your seated meditation, or throughout one's day while driving or working, is to repeat to yourself, "I am calm and peaceful".
One of the most well known and most ancient forms of Mantra Meditation is to chant, say, or think the word "Om" while meditating. Om is considered to be one of the most sacred mantras and is frequently used at the beginning of other sacred prayers or mantras, such as Om mani padme hum, a well known mantra used in Hindu and Buddhist prayer and meditation.
The great thing about using Mantra Meditation is that you can customize it to your personal needs. For instance, if you are working on building your self esteem, you can meditate while focusing on the phrase, "I value myself. I value others. I value the world". Or if you are working on your own anger management you can use a metta meditation which goes something like this: "May all beings be happy. May I be happy. May all beings be peaceful. May I be peaceful. May all being be free. May I be free", etc. You get the picture.
Mantra meditation is very powerful. One of the most powerful things it does is keep you from running the usual flow of negative thoughts that may traditionally run through your mind. It's a very conscious and intentional practice and with time you can get very good at it.
Thanks to Hartwig HKD for the great photo - Amitabha