Manah prasamanopayah yoga ityabhidhiyate
A skill to calm down the mind is called yoga

Manah = mind; Prasamana upayah =calming down skill; Yoga = yoga; Iti abhidhiyate = (it is) so called.

Sama is to calm down. Prasamana is to deeply calm down, tranquil, pacify. If concentration is one dimension of mastery over the mind, tranquilling or pacifying or calming down the mind the second dimension. This is what we have missed in modern times. In our new educational system we have been trying to sharper the mind, enhance the power of the intellect analysis power, thinking power, etc. We have become very sharp and sensitive. But this very sensitivity and sharpness have started cutting us down. Anxiety stress, tension descends down to physical frame causing hyper sensitivities and allergies, manifesting in the society as student unrest, drug culture, divorces, gun culture and terrorism, etc. We have grown lopsided - gigantic in developing our sharpness, analytical and critical faculty but are pigmies in silencing our mind. It is this second dimension which is most needed for the modern man Yoga is that systematic science to harness this power within us.