Nikon no tokudo (耳根の得道)
Nikon no tokudo refers to attain Nirvana and salvation (Jodo (completing the path to becoming a Buddha by attaining enlightenment)) by listening to the chanting of Myohorenge-kyo Sutra (the Lotus Sutra). Nikon' is one of the five roots comprising eyes, ears, a nose, a tongue, and the body, and refers to the organ itself and its ability to pick up voice and sound.
In Nichiren's words (gosho (writings)), it is described as follows.
The world we live in is the realm of nikon no tokudo, and all the people can learn Myoho (excellent methods) through voice, and attain the mental state of entrance into Nirvana through ascetic practices.