A yogi is a practitioner of Yoga, including a sannyasin or practitioner of meditation in Indian religions. The feminine form, sometimes used in English, is yogini.
Bronze figure of a yogi in Dhyana (meditation) by Malvina Hoffman
A 10th-century Yogini statue from Tamil Nadu, India. She is seated in an asana, and her eyes are closed in meditative state.
Shiva in the form of Adiyogi (or first yogi) in Coimbatore, India
A sculpture of Gorakhnath, a celebrated yogi of Nath tradition and a major proponent of Hatha yoga.
Sadhu is a religious ascetic, mendicant or any holy person in Hinduism and Jainism who has renounced the worldly life. They are sometimes alternatively referred to as yogi, sannyasi or vairagi.
Yogi
…According to David White, [S]iddha means 'realized, perfected one', a term generally applied to a practitioner (sādhaka, sadhu) who has, through his practice (sadhana), realized his dual goal of superhuman powers (siddhis, 'realizations', 'perfections') and bodily immortality…
Two sadhus near Pashupatinath temple in Kathmandu
Sadhu in Pashupatinath Temple, Kathmandu, Nepal.
A sadhu in yoga position, reading a book in Varanasi
A female sadhvi with a Vishnu mark on her forehead