The Sanskrit word yoga means add, unite, or attach Yoga can be defined as the link between body, breath and mind. Modern meanings include endeavour and diligence.
Hatha Yoga focusses on posture, breath and bodily health. The basic principles of Hatha yoga were collected by Yogi Swatmarama in the Hatha Yoga Pradipika in 15th century. Hatha Yoga includes both physical and breath training and aims to build strenth, flexibility and self-control.
In the West the 4 aspects of hatha yoga most commonly practiced are:
Asana (Physical poses) is designed to create a balance of strength and flexibility which leads to good general health.
Pranayama (Breath control) is a series of breathing exercises which increase lung capacity, lower heart rate and create mental focus.
Bhanda (Core Stability). A set of exercises to build strength in the abdominal and pelvic floor muscles - great for supporting the lower back.
Dharana - Mindfulness or self-awareness. Alleviates stress and helps concentration.
Raja Yoga focuses on the mental and spiritual aspects of yoga. It was first described in the early centuries CE in the Yoga Sutras of Patanjali which define the purpose of yoga as citta-vṛtti-nirodhaḥ (the cessation of the peturbations of the mind)