Shinjin was originally the Japanese word for the Buddhist concept of citta-prasāda (clear or clarified heart-mind), but now carries a more popular related meaning of faith

Faith

Faith is confidence or trust in a person or thing, or a belief that is not based on proof. In religion, faith is a belief in a transcendent reality, a religious teacher, a set of teachings or a Supreme Being. Generally speaking, it is offered as a means by which the truth of the proposition,...

 or entrusting.

Whilst a general Japanese Buddhist term it is particularly associated with the Jodo Shinshu

Jodo Shinshu

, also known as Shin Buddhism, is a school of Pure Land Buddhism. It was founded by the former Tendai Japanese monk Shinran. Today, Shin Buddhism is considered the most widely practiced branch of Buddhism in Japan.-Shinran :...

 teaching of Shinran

Shinran

was a Japanese Buddhist monk, who was born in Hino at the turbulent close of the Heian Period and lived during the Kamakura Period...

. In that context it refers to the awakening and settlement of the mind that is aware of the working of Amida

Amida

Amida can mean:* Amitabha, an important Buddha in East Asian Buddhism* Amida , a beetle genus* Amida Buddha* Amidah, the central prayer of the Jewish services* Amidakuji, a way of drawing lots* Amitabh Bachchan, an actor...

 Buddha

Buddha

In Buddhism, buddhahood is the state of perfect enlightenment attained by a buddha .In Buddhism, the term buddha usually refers to one who has become enlightened...

's Primal Vow

Primal Vow

The Primal Vow , also known as the 18th Vow is part of a series of 48 vows that Amitabha Buddha made in the Larger Sutra of Immeasurable Life...

, and the assurance of birth in the Pure Land

Pure land

A pure land, in Mahayana Buddhism, is the celestial realm or pure abode of a Buddha or Bodhisattva. The various traditions that focus on Pure Lands have been given the nomenclature Pure Land Buddhism. Pure lands are also evident in the literature and traditions of Taoism and Bön.The notion of 'pure...

at death:

In Notes on 'Essentials of Faith Alone Shinran writes "Know that the true essence of the Pure Land teaching is that when we realize true and real shinjin, we are born in the true fulfilled land."