-Hatha Yoga Pradipika
The Sanskrit word mudra means gesture or attitude. Mudras can be described as psychic, emotional, devotional and aesthetic gestures or attitudes. Attitudes of energy flow, intended to link individual pranic force with universal or cosmic force.
The Kularnava Tantra traces the word mudra to the root mud, meaning delight or pleasure, and dravay to draw forth.
Mudras are a combination of subtle physical movements which alter the mood and deepen the awareness and concentration.
The Hatha Yoga Pradipika consider mudra to be an independent branch of yoga. They are introduced after some proficiency has been attained in asana, pranayama and bandha and gross blockages have been removed.