Kosa means "layer of mind".
There are five layers of the human mind, in addition to the physical body, which – although technically not a kosa itself – is given the name Annamaya ("food") Kosa. Its natural means of development is through diet and physical exercise. In Ananda Marga practice it is also developed through asanas, Tandava and Kaoshikii.
The mind is composed of five layers, just like the banana flower. Shrii Shrii Anandamurti
1. The Crude Mind is called the Kamamaya Kosa. Kama means "desire." It is this most superficial layer of mind that is responsible for attraction and aversion to sensory stimuli, and the physical reactions to those stimuli. It is developed naturally through physical clash, and for sadhakas (spiritual practitioners) by following Yama and Niyama.
2. The Subtle Mind is called the Manomaya Kosa. Man means "to think", and it is this layer of mind which gives the experience of pleasure and pain through thought, memory and dreams. This kosa is developed naturally through physical clash, and in Ananda Marga sadhana by pranayama with cosmic ideation.
The next three deeper layers of mind are collectively known as the Causal Mind. Causal signifies that these layers are in the most direct contact with the Causal Consciousness from which the mind has evolved and within which it exists.
3. The first layer of the Causal Mind is the Atimanasa Kosa – the Supramental Mind. This is the intuitive layer, which gives the capacity for such phenomena as intuitive dreams, clairvoyance, telepathy and creative insight. Its natural means of development is through psychic clash, and in Ananda Marga sadhana by methods of pratyahara (withdrawal) such as shuddhis and Guru Puja.
4. The second layer of the Causal Mind is the Vijinanamaya Kosa, or Subliminal Mind. Vijinana means "special knowledge," and includes many higher qualities of mind such as viveka (conscience, or discrimination – the ability to determine right from wrong) and vaeragya (non-attachment – the realization that it is unwise to be attached to any limited entity). The natural development of this kosa is through psychic clash, and its development is accelerated by the process of dharana.
5. The most subtle layer of the Causal Mind is the Hiranyamaya ("golden") Kosa, the Subtle Causal Mind. Here the awareness of mind is very close to the direct experience of Supreme Consciousness. There is only the separation of a thin veil of ignorance. Its natural development is through attraction for the Great, and dhyana accelerates this process for sadhakas.
The lessons of Ananda Marga meditation develop all layers of the mind in a balanced manner.
The development of mind is a process of clash and cohesion. Whenever an action is performed it creates an impression, or potential reaction, in the mind. This is called samskara – the distortion of mind waiting for expression. In order to express one's samskaras, different experiences (some pleasurable and others painful) will have to be encountered, depending on the samskaras to be expressed. But regardless of whether the experiences are pleasurable or painful, from a spiritual viewpoint they are always desirable because they facilitate the exhaustion of one's samskaras – hence the purification of mind and consequent increased desire for cosmic merger. So obstacles and hardship are considered beneficial on the spiritual path. For the optimal progress, therefore, spiritual practice must be combined with worldly struggle, and this preferably in the form of social service.
It is a bigger thing to put one lesson into action than to hear many. You should put into action every lesson of your life. Shrii Shrii Anandamurti