Today, Yoga (योग) is popular mostly as another form of fitness or gymnastics. But physical postures, also called Asanas (Āsana आसन) are just a small portion of Yoga.
In the traditional form of Yoga, Asanas were primarily used as a way to prepare the body for long periods of meditation.
Yoga is in reality a way of living. And a good way to show what yoga really represents is by introducing the classification of Yoga found in The Yoga Sutras of Patanjali : The Eight Limbs of Yoga, or Ashtanga (Aṣṭāṅga अष्टाङ्ग) Yoga (Ashta = eight ; Anga = limb) as it shows eight stages in the path of Yoga that require a lifetime (or more) to be fully integrated.
1st limb : YAMA (यम)
Physical level
Outer world
Suppression
Self-restraint
Five social and ethical rules of conduct :
Ahimsa (Ahiṃsā अहिंसा) : Non-violence ; Not harming or injuring others ; Kindness ; Compassion ; Safeness ; Security
Satya (सत्य) : Truth ; Sincerity ; Honesty ; Goodness ; Purity ; Knowledge
Asteya (अस्तेय) : Not-stealing from others (ideas, time, energy)
Brahmacharya (brahmacarya ब्रह्मचर्य) : Conduct of Brahman ; Moderation ; Continence ; Chastity ; Sexual integrity
Aparigraha (अपरिग्रह) : Non-possessiveness ; Renouncing ; Deprivation ; Renunciation ; Destitution ; Poverty ; Generosity
2nd limb : NIYAMA (नियम)
Physical level
Inner world
Suppression
Self-restraint
Five personal and spiritual rules of conduct :
Shaucha (Śauca शौच) : Cleanliness ; Self-purification on the physical and mental levels ; Evacuation of excrement
Santosha (santoṣa सन्तोष) : Contentment ; Joy ; Satisfaction ; Practice of being happy
Tapas (तपस्) : Austerity ; Perseverance ; Asceticism ; Pain ; Suffering ; Exposing ourselves purposefully to a challenging situation while keeping our mind calm.
Swadhyaya (Svādhyāya स्वाध्याय) : Repetition of Mantras ; Self-study ; Study of any holly book or sacred text (like the Veda), or any other subject, in order to learn
Ishvara Pranidhana (Īśvarapraṇidhāna ईश्वरप्रणिधान) : Devotion to God (or the unknown) ; Prayer to the Lord (the Supreme Soul) ; Giving up our personal effort because we can not do more, and letting some other force (human, animal, nature, or divine help) carry us along ; Surrendering to God, or the unknown, doesn't mean demanding.
3rd limb : ASANA (Āsana आसन)
Pysical level
Body
Posture practice
Asana helps remove physical & mental toxins that create stiffness & tension in the body (muscles, blood, skin, bones, fascia, ...)
"Sthira Sukham Āsanam" : "The posture must be steady and comfortable" (YS II:46)
4th limb : PRANAYAMA (Prāṇāyāma प्राणायाम)
5th limb : PRATYAHARA (Pratyāhāra प्रत्याहार)
Physical level
Indriya (इन्द्रिय) = Five sense organs (eyes, nose, ears, tongue, skin)
Abstraction
Retreat
Drawing back
Withdrawal of the senses
Dissolution of the outer world
Controlling the mind by overcoming sensory distractions (sound, smell, touch, sight, taste).
Turning our awareness inward, within ourselves. (YS II:54)
6th limb : DHARANA (Dhāraṇā धारण)
Mental level
Conscious state
One-pointed Concentration
Fixing our attention upon one point, object, or idea. After a while, when we close our eyes, we should be able to bring a mental picture of the object of concentration. (YS III:1)
7th limb : DHYANA (Dhyāna ध्यान)
Mental level
Unconscious state
Seeing with the mind's eye
Reflection
Contemplation
Meditation
8th limb : SAMADHI (Samādhi समाधि)
Mental level
Superconscious state
Accomplishment
Being Whole
Pure Bliss
In Constant Harmony with the Universe
Union between Atman (individual soul) and Brahman (Universal Soul), which is the goal of Yoga.