Astral Projection

An Astral Projection (アストラルプロジェクション) is a willful, where one's consciousness separates from their physical body as an Yūtai (幽体) and travels elsewhere.

In Toaru Majutsu no Index, astral projections are possible through applications of Magic.

Principles
While the astral body is separate from the physical body, the latter is unable to defend itself and requires external protection.

are one tool used to achieve astral projections. Robert William Felkin (or at least his reproduction) makes use of tattva-based mental immersion spiritual items, which Aleister Crowley guessed were meant to drag other people's minds into the bog, with his group working together to attack the enemy's defenseless physical body once the astral body had been removed.

Background
During one talk with Mina Mathers in the past, on the subject of a lack of money to get through the month, Samuel Liddell MacGregor Mathers mentioned that he could separate himself from his physical bonds and go on an astral journey should things come to it.

Coronzon Arc
Astral projections were referenced several times during the events involving the reproduced Golden Dawn,   with several members, including Annie Horniman and Mathers, using some methods of communication which appeared somewhat similar but were a bit more primitive, vibrating magic power at a set frequency in order to make contact.