Siddhasana or Accomplished Pose is a Yoga

Yoga

Yoga is a physical, mental, and spiritual discipline, originating in ancient India. The goal of yoga, or of the person practicing yoga, is the attainment of a state of perfect spiritual insight and tranquility while meditating on Supersoul...

 asana

Asana

Asana is a body position, typically associated with the practice of Yoga, originally identified as a mastery of sitting still, with the spine as a conduit of biodynamic union...

.

Etymology

The name comes from the Sanskrit words siddha (सिद्धा; siddhā) meaning both "perfect" and "adept", and asana (आसन; āsana) meaning "posture" or "seat".

Description

From a seated position, one heel is brought to the groin area (perineum

Perineum

In human anatomy, the perineum is a region of the body including the perineal body and surrounding structures...

), then the opposite ankle placed over the first with the toes and heel of the second foot resting in the fold between the thigh and calf of the first leg beneath it. The spine

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

 is held erect. A small meditation cushion or zafu

Zafu

A zafu is a round cushion. Although also a utilitarian accessory, it is most well known for its use in zazen Zen meditation.-Name:...

is sometimes used to aid vertical back alignment.

Usage

Siddhasana and Padmasana (Lotus Pose) are the two asanas traditionally used for dhyana

Dhyana in Hinduism

According to the Hindu Yoga Sutra, written by Patanjali, dhyana is one of the eight limbs of Yoga, ....

 (meditation) and pranayama

Pranayama

Pranayama is a Sanskrit word meaning "extension of the prana or breath" or more accurately, "extension of the life force". The word is composed of two Sanskrit words, Prāna, life force, or vital energy, particularly, the breath, and "āyāma", to extend, draw out, restrain, or...

 (breath) exercises. Sukhasana

Sukhasana

Sukhasana , Easy Pose, Decent Pose, or Pleasant Pose, is an asana practised in yoga, buddhism and hinduism, similar to sitting in a simple cross-legged position. While opening the hips and lengthening the spine, the posture's relative ease on the knees makes it easier than siddhasana or padmasana...

 (Pleasant Pose) is a substitute that is easier on the knees.

The Hatha Yoga Pradipika

Hatha Yoga Pradipika

The Hatha Yoga Pradipika is a classic Sanskrit manual on hatha yoga, written by Svami Svatmarama, a disciple of Swami Gorakhnath. Said to be the oldest surviving text on the hatha yoga, it is one of the three classic texts of hatha yoga, the other two being the Gheranda Samhita and the Shiva...

asks,

When siddhaasana is mastered, of what use are the various other postures?