In Hinduism, a sādhu (Sanskrit: साधु sādhu, “good; good man, holy man”) is a religious ascetic or holy person. Although the vast majority of sādhus are yogīs, not all yogīs are sādhus. The sādhu is solely dedicated to achieving mokṣa (liberation), the fourth and final aśrama (stage of life), through meditation and contemplation of brahman. Sādhus often wear saffron-coloured clothing, symbolising their sanyāsa(renunciation). This way of life is open to women; the female form of the word is sādhvī साध्वी. In 2014 an all-female akhada (group of sadhus) was formed; it is believed to be the first such group in India.
The Sanskrit terms sādhu (“good man”) and sādhvī (“good woman”) refer to renouncers who have chosen to live a life apart from or on the edges of society to focus on their own spiritual practice.
The words come from the Sanskrit root sādh, which means “reach one’s goal”, “make straight”, or “gain power over”. The same root is used in the word sādhana, which means “spiritual practice”. ‘Sadhu’ can also be used as Vidhyartha, meaning ‘let good happen’.
Excerpt from Wikipedia