An energetic canal within the spinal column.
“The seven churches are similar to lotus flowers that are suspended from the famous Chitra Nadi. The canal of Shushumna exists within the medullar canal. The canal of Chitra Nadi is within this canal of Shushumna.” - Samael Aun Weor, The Aquarian Message
“Within this Sushumna there is a Nadi by name Vajra which is lustrous as Surya (sun) with Rajasic qualities. Again within this Vajra Nadi, there is another Nadi, called Chitra. It is of Sattvic nature and of pale colour. The qualities of Agni, Surya and Chandra (fire, sun and moon) are the three aspects of Sabda Brahman. Here within this Chitra, there is a very fine minute canal (which is known as Canalis Centralis). This canal is known as Brahmanadi through which Kundalini, when awakened, passes from Muladhara to Sahasrara Chakra. In this centre exist all the six Chakras (lotuses, viz., Muladhara, Svadhishthana, Manipura, Anahata, Vishuddha and Ajna). The lower extremity of the Chitra Nadi is called Brahmadvara, the door of Brahman, as Kundalini has to pass through this door to Brahmarandhra. This corresponds to Haridwar which is the gate of Hari of Badrinarayan in the macrocosm (physical plane). The Chitra terminates in the Cerebellum. In a general sense the Sushumna Nadi itself (gross Spinal Cord) is called Brahma Nadi because, Brahma Nadi is within the Sushumna. Again the canal within the Chitra is also called Sushumna, because the canal is within the Sushumna. Ida and Pingala Nadis are on the left and right sides of the spine. Chitra is the highest and most beloved of the Yogins. It is like a thin thread of lotus. Brilliant with five colours, it is in the centre of Sushumna. It is the most vital part of the body. This is called the Heavenly way. It is the giver of Immortality. By contemplating on the Chakras that exist in this Nadi, the Yogi destroys all sins and attains the Highest Bliss. It is the giver of Moksha.” - Swami Sivananda, Kundalini Yoga