Meditation refers to a broad range of techniques that involve some form of physical or mental self-regulation and "present moment" focus. Meditation is an element of almost all religions and has been practiced for more than 5,000 years.
There are two higher order types of meditation that encompass most other forms -- they are called "concentrative" meditation and "mindfulness" meditation. There are many forms of meditation that integrate the two.
Concentrative meditation is the most common form of meditation. It involves limiting outside stimulus by directing attention to a single or narrow focus (such as your breathing, or a mantra). By concentrating on a single stimulus, the mind can become free of distraction.
Mindfulness meditation encourages the cultivation of a present-moment, non-judgmental sustained awareness of your thoughts, feelings, behaviors and environment. It is specifically intended to remove analytical thought or analysis. Unlike concentrative meditation, it is about fluidity of thought rather than distraction.
Traditionally, meditation was used for spiritual growth. Today, however, it is being used to improve health and performance. Today's meditation typically involves body awareness, usually through breath "retraining," or techniques that reduce "ruminative" thoughts.