Esoteria is a form of aether that is actually knowledge or information from a biological brain stored as magic. It takes a great magic-user to transform esoteria back into workable ideas within a mind.
Esoteria is a form of aether, so it has no physical form, that is actually a memory or piece of knowledge or idea. Given a powerful magic-user, they could transform esoteria back into an idea within their own minds. Esoteria is used by old and powerful magic-users who are still limited by biological brains, with limited memory retention. A user can store the esoteria within something, such as a box, to take it wherever they go and access it[Tales 1].
See also: Ameryl Hypericum
Ameryl Hypericum was partially involved with the intelligence division of The Imperium, especially after she rose high within its ranks and her friendship with Gadreel, the Watcher, grew. As her position came to rely heavily on knowledge and spying, she started to store her memories and informations as esoteria and was one of the rare few capable of turning the information back into thoughts[Tales 1].