Definition - What does Sadhu mean?
A sadhu is a Hindu ascetic who has decided to leave all material attachments and dedicate his life to achieving spiritual liberation, or moksha. They usually wear special clothing as a symbol of their sannyasa, which is a HIndu term for renunciation. The female equivalent of a sadhu is a sadhvi.
Sadhus are often yogis, although not every yogi is a sadhu. They may also be called baba, which translates as "father," "grandfather" or "uncle." There are between four and five million sadhus in Nepal and India today, living in the caves and woods and having no material possessions.
There are many different types of sadhus, relating to different types of religious practices, but there are two main lines of sadhus: Shaiva sadhus devoted to the Hindu god, Shiva, and Vaishnava sadhus, who are devoted to Vishnu.
Yogapedia explains Sadhu
Being a sadhu is the fourth stage of the life of a Hindu, after studying, parenthood and pilgrimage.
There are different processes of becoming a sadhu within the different Hindu sects. They are usually initiated by a guru, given a new name and their own mantra. The mantra usually remains secret, known only to the master and the sadhu. Although some practices of the sadhus might seem extreme - such as being silent for years, sitting in a cave for a long time, or standing on one leg for many years - others include practices such as Hatha yoga, devotional worship of a deity, or meditation practices.
Sadhvis start their hermit life after the death of their husband and often live in isolation and ascetism. In some sects, sadhvis are considered a form of a goddess and are worshipped.