bhramari pranayama

A very calming yogic breathing practice, also known as “humming bee breath,” that soothes the nervous system and helps to connect us with our truest inner nature; this practice consists of inhaling into the belly and exhaling while making a humming sound at the back of the throat—like the gentle humming of a bee.

Source: http://www.banyanbotanicals.com/info/ayurvedic-living/learning-ayurveda/glossary-of-ayurvedic-terms/