While there may be dozens of ways of doing meditation, if we organize them by brain-wave then there are 4 major types of meditation:
Alpha wave is the most common type, it is a relaxed state, the same state you naturally go into when you close your eyes for a few minutes. Alpha-wave meditations are good for refining your consciousness. It is the gateway to all other forms of meditation.
Theta-waves are commonly found in children when they are learning, it is called “passive-alert”. This particular brain-wave frequency range is the best of passively assimilating new knowledge, adults and teens which need to study may benefit from cultivating this stage when reading or watching something new. This brain-wave frequency range is also when it is easiest to work with the subconscious.
Delta-waves are prominent during deep-sleep where the body heals itself, where new neuron connections grow. Some older people have trouble getting deep sleep, so delta-wave meditations can help with both getting deeper sleep, healing the body and mind. Various void meditations help with this.
Gamma-waves are found in individuals that have high IQ’s or are high performance athletes and other people that are good at solving problems. Amongst meditators it is most common in those that do Compassion Meditation. Divine Meditation is known to improve cognitive performance.