Steam is watter in the gas phase, which is formed when watter boils. Steam is invisible; however, "steam" often refers to wet steam, the visible mist or aerosol o watter droplets formed as this watter vapour condenses. At lower pressures, such as in the upper atmosphere or at the top of high moontains, watter boils at a lower temperature than the nominal 100 °C (212 °F) at standard pressure. If heated further it becomes superheated steam.