Agni Sara is one of the Shat kriyas (six cleansing processes). It is the counteraction to Uddiyana Bandha Kriya or Nauli. Agni means fire - we are invigorating our digestive fire.
The stomach is expanded on an exhale with the breath held out. We are giving space to our internal organs allowing the free flow of substances and energy. Very beneficial for digestion and health of the digestive organs.
Contraindication, do not do this pranayama if you are pregnant or on your menstrual cycle.