In Buddhist cosmology, the realm of the asuras (demigods), characterized by constant conflict and jealousy. Often contrasted with the heavenly realms.
The Asura realm is one of the six realms in Buddhism, said to be a world of unending conflict.
六道 is the broader concept of the six realms of existence in Buddhism, of which 修羅界 is one.
From 修羅 (shura, 'asura') + 界 (kai, 'realm, world'). 修羅 is a transliteration of Sanskrit 'asura'.