In the sramanic traditions of ancient India (most notably those of Mahavira and Gautama Buddha) arhat (Sanskrit) or arahant (Pali) signified a spiritual practitioner who had—to use an expression common in the tipitaka—"laid down the burden"—and realised the goal of nibbana, the culmination of the spiritual life (brahmacarya). Such a person, having removed all causes for future becoming, is not reborn after biological death into any samsaric realm.
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[Japanese] The Japanese term for the arhats, or Buddhist saints, who have already become perfect in this life. It refers particularly to the 500 immediate disciples of Gautama, the historic Buddha.