Raja/Ashtanga yoga

Patanjali’s Yoga Sutras (written at least 1800 years ago), laid out eight principles which govern the physical, moral and spiritual conduct of yogis:

Yama (ethics)
Niyama (self-control) 
Asana (physical yoga practice)
Pranayama (breathwork)
Pratyahara (sensory withdrawal)
Dharana (concentration)
Dhyana (meditation) 
Samadhi (enlightenment or peace)

The asanas are just one aspect of what makes a yoga practice, and can be seen as a metaphor for living life. The asanas represent life and the ease or struggle; challenges or opportunities with which we deal with them.  Enlightenment can mean finding acceptance and being at peace with ourselves and the world around us.