A Hinayana practitioner during the dark ages when the teachings of a Buddha are not available.
Literally, "self-realizers" or "self-evolvers" - practitioners of the Hinayana vehicle who, motivated by renunciation, strive to attain liberation from uncontrollably recurring rebirth (samsara) and to become an arhat (liberated being). They live during dark ages when the teachings of a Buddha are no longer available. They do not study with Buddhist spiritual teachers, because there are none at such times, and they teach others only subtly, through gestures, since people are not receptive. Living either singly ("like a rhinoceros") or in small groups, they must rely on their instincts from previous lives to recall and master the Dharma. Some translators render the term as "solitary Buddhas."
J Hopkins: Solitary Realizer.