Sealing (封印, Fūin) is a special ability in which allows the ability to inhibit an individual.
When sealing magic like that of magics derived from the demon eye, unknown but special markings are placed on a rag in which is then bound to an individual (in this case, around their eyes). These markings make it impossible to utilize magic until it is removed.
While users may be capable of sealing individuals even as powerful as a Kishin, there comes to be some sort of major cost; sealing a powerful true god seems to somehow require the likes of a goshitai to have been made for sealing them as well as various tags with special marking on them made. Sealing a powerful entity such as a god comes to a great sacrifice: the user can only move from within the limits of their soul and the sealing must be maintained.