Some musicians spend long periods of their training in varying degrees of isolation and describe these as their chilla; for others, it's a shorter, more extreme retreat, traditionally lasting 40 days.
The word Chilla in music comes from the practice of forty days after childbirth during which the mother is said to be "unclean", or quarantined, or more generally a period of religious fasting and worship.
[1] The musicians lock themselves up in a solitary cell called chilla-khana for forty days and practice their instrument severely.
[2] Abdul Karim Khan, a singer of the Kirana Gharana, described chilla as "lighting a fire under your life.
This was the famous Ghalib couplet, late Sitar maestro Ustad Abdul Halim Jaffer Khan often quoted, to sum-up the intensely grueling process of becoming a successful Hindustani musician.