Soma is an ancient Vedic deity opposite Agni or fire in nature. Soma refers to water and the receptive principle on all levels, including the cosmic ocean of space and bliss. Agni indicates fire and light, including the illuminating principle on all levels to the highest transcendent awareness.
As Agni is the Sun, Soma is the Moon. As Agni the the perceptual aspect of consciousness, Soma is the receptive aspect, including the mind and senses at an outer level.
Traditional Yoga, extending to Kundalini Yoga, is a process of balancing the different forms of Agni and Soma within us, notably the Agni of the Muladhara, the earth or root chakra, the ascending Kundalini Fire, with the nectar or amrit, the descending Soma of the crown chakra or lotus of the head.
Yet there were also important botanical Somas, mainly powerful mountain-growing plants of various types, including different reed grasses, orchids, lilies, vines, lotus and lily plants. Ultimately Soma is the healing essence (rasa) of all the plants, connected to plant juices, honey, oils and even milk and ghee, notably their rejuvenating or rasayana factors for body and mind.
The following audio by Dr. David Frawley explores the botanical aspect of Soma in light of its cosmic and yogic symbolism, which is seldom understood or presented anywhere. Understanding Soma is essential in Yoga and Ayurveda for achieving Self-realization, Samadhi and Ananda in Yoga, and for rejuvenation of the mind and brain (Medhya Rasayana) along with overall longevity and wellbeing in Ayurveda. How to connect with these transformative Somas is one of the great secrets of the Vedic Rishis.