(Japanese) Spell, incantation.
Jumon is a sound that invokes a specific energetic vibration. In modern forms of the system of Reiki it is commonly called by the Sanskrit word mantra.
In Mikao Usui’s early teachings it is said that the jumon made the teachings more accessible for Shintô followers. They can be used as a focus point for meditation.
According to Suzuki san, it was Toshihiro Eguchi who introduced the three okuden jumon to Mikao Usui.