An eruption or flow of drilling mud from a wellbore resulting from the entry of formation fluids, oil, gas, or water into the borehole. Such entry occurs when the pressure in the borehole does not counterbalance the pressure in permeable formation.An eruption or flow of drilling [[mud]] from a [[well bore|wellbore]] resulting from the entry of [[formation]] fluids, oil, gas, or water into the borehole. Such entry occurs when the [[pressure]] in the borehole does not counterbalance the pressure in permeable formation.