The Illuminator Dictionary from Tony Duff has a really good excerpt on this:
"Pratyekabuddha", "solitary realizer" or "self-made buddha". The disciples of the Buddha who followed the teachings of the ཐེག་པ་དམན་པ་ Lesser Vehicle were of two kinds: Śhrāvakas and Pratyekabuddhas. The Śhrāvakas listened to the teaching and taught it to others, the Pratyekabuddhas having heard the teaching went off and obtained their realization in solitary practice.
The term "pratyekabuddha" in Sanskrit comes from the two Sanskrit words "pratyeka" and "buddha" meaning that they "on their own" became "buddhas". This was translated completely accurately in Tibetan with རང་ and སངས་རྒྱས་ which were then combined into རང་སངས་རྒྱས་. The definition of the term as it was passed from India to Tibet is as follows. A Pratyekabuddha is explained as someone who without having an ongoing relationship with an āchārya (unlike the ཉན་ཐོས་ Śhrāvakas), manifested their རང་ own enlightenment through their own prajñā and hence were that type of སངས་རྒྱས་ buddha. This is captured well with the English "solitary realizer" or "self-made buddha". Another common term for རང་སངས་རྒྱས་ is རང་རྒྱལ་ "Solitary Conqueror"; sometimes the two are put together to be རང་སང་རྒྱས་རང་རྒྱལ་ "solitary realizer, solitary conqueror".
There are two styles of behaviour amongst pratyekabuddhas: those who live in isolation and practice their path in a completely solitary way and those who do their practice while mixing with society:
A foolish man proclaims his qualifications,
A wise man keeps them secret within.
A straw floats on the surface of water,
But a precious gem placed upon it sinks to the depths