What is Bonji in Japanese Katana terminology?

The term "Bonji" (梵字, ぼんじ) refers to the Sanskrit characters used in the design to represent Buddhist deities. These are often seen in the carvings on the body of a Japanese sword. Originating in India, these characters are believed to have been created by "Brahma", the creator of all things, and have been engraved on the body of Japanese swords from the earliest times as objects of faith.