Definition - What does Vajra Nadi mean?
In Hindu and yogic philosophy, the vajra nadi is part of the network of pathways through which life force energy travels in the body. The name comes from the Sanskrit, vajra, which means “firmness,” “thunderbolt" and “adamant.” Nadi means “channel,” “tube” or “flow.”
Three major nadis follow the length of the spine. They are the sushumna nadi (central channel), the ida nadi (left channel) and the pingala nadi (right channel). The vajra nadi is the first layer of subtle nadis located within the sushumna nadi.
Yogapedia explains Vajra Nadi
Vajra is associated with the sun and with energy and ambition. Located within vajra is the chitra nadi, and within chitra is the brahma nadi, which is the subtlest nadi and is believed to contain the main chakras, or spinning circles of life force energy. The vajra nadi is said to activate the powers of each of the chakras as the kundalini, or primal energy, awakens and rises through the nadis.
The vajra nadi begins in the muladhara (root) chakra. Within vajra, the chitra nadi contains an entryway called brahmadvara through which the kundalini passes when it is awakened. It then travels through the brahma nadi. The yogic practices of pranayama, meditation and mantra chanting help to awaken kundalini and circulate it through the nadis.