There are three worlds of existence: the physical, the subtle, and the causal, termed Bhuloka, Antarloka, and Shivaloka.
The physical plane, or Bhuloka, is the world of gross material substance in which phenomena are perceived by the five senses. It is the most limited of the worlds, least permanent, and the most subject to change. The material world is where we have our experiences, manufacture karma and fulfill the desires and duties of life in a physical body. It is in Bhuloka that consciousness is limited, that awareness of the other two worlds is not always remembered.
The subtle plane, or Antarloka, is the mental-emotional sphere that we function in through thought and feeling and reside in fully during sleep and after death. It is the astral world that exists within the physical plane. The astral plane is for the most part exactly duplicated in the physical plane, though it is of a more intense rate of vibration.
The causal plane, or Shivaloka, pulsates at the core of being, deep within the subtle plane. It is the superconscious world where God and highly evolved souls live and can be accessed through yoga and temple worship. The causal plane is the world of light and blessedness, the highest of the heavenly regions, extolled in the scriptures of all faiths.
It is the foundation of existence, the source of visions, the point of conception, the apex of creation, abode of Lord Shiva Himself. The Shivaloka is the natural refuge of all souls.
(The above is taken from Jan/Feb/Mar 2013 issue of Hinduism Today)