Santosha

Santosha means 'contentment'.  They are the moments when you feel blissful, and these moments are pretty rare.  It is possible to find 'santosha' in your asanas when you practice with diligence and full awareness of your movements.  Moving with intelligence, strength, elequonce and beauty in sychronisation with your breath.  It brings a sense of calmness and focus into the present moment.  It is the energy you feel that settles and grounds you for the rest of the day. 
 

Here's a good article I thought explain it in one of the best ways possible from Yoga Journal about 'prana' and the goodness of it all

".....you can learn to tune in to prana when you're awake and to build reserves of it.When you remove obstacles to free-flowing prana, you feel more alive and present in your life. Think of how great you feel after a yoga class or a night of dancing or making love. Movement can awaken both prana and awareness. Slow-motion movement slows your mind. Just a few minutes of it before sitting is an excellent segue to a more subtle meditation practice. Try lifting your arms overhead and slowly releasing them to your sides, concentrating on the micro-movements of your hands as they flow through space. Just a minute of this helps you move into pratyahara, sense withdrawal.
Paying attention to slowing down helps you be mindful during the day. Try brushing your teeth or washing dishes more slowly and see how that brings your mind into the present. Slowing down a yoga pose also helps draw you into a dynamic flow of sensation, breath, and awareness.
A fascinating paradox emerges when you allow yourself to become absorbed in the small details of any physical action. Embracing movement, you are inexorably drawn to the stillness within." (Jonathan Foust, M.A)

 "Om" to that :)