Union of the Individual Soul and Supreme Soul is called Yoga.
योग: चित्तवृत्ति निरोध:
(To control the frequency of the Thought process is called Yoga).
Yoga described by Maharshi Patanjali is called Patanjali Yoga and He mentions there are eight limbs to get Self-Realisation.
According to His eights limbs it is called Ashtanga Yoga.
The eight limbs are below;
Yama (How we behave in Society)
Niyam (How we live in the Society)
Asana (Physical Exercise)
Pranayama (The Breathing Exercises)
Pratyahara (Withdraw the Senses Inwards)
Dharana (Concentrate the Mind on your Own-Self)
Dhyana (Continuously concentrate the Mind on your Own-Self is called Meditation)
Samadhi (Liberation)
When the Mind will merge on your Own-Self is called Self-Realisation.
This Physical Body has more inter connection with Breathing, Breathing more inter connection with Senses, Senses more inter connection with the Mind. Mind more inter connection with the Intellect. Intellect more inter connection with the Soul. These all are the inter combination to get Self-Realisation from Physical Body towards Supreme Soul. From Yama upto Pratyahara Bahiranga Sadhana (External Efforts) is called Hatha Yoga. From Dharana upto Samadhi is called Antaranga Sadhana (Internal Efforts) is Raja Yoga.