The document discusses atmospheric moisture and its impacts. It describes the hydrologic cycle which governs the movement of water across Earth. Water exists in three phases - solid, liquid, and gas - and undergoes phase changes through processes like evaporation, condensation, and sublimation. Various measures of humidity quantify the amount of water vapor in air, including relative humidity. Clouds form through condensation and influence climate. Precipitation forms through processes like collision-coalescence and the Bergeron process. Global precipitation patterns are uneven, with wet tropical regions and dry deserts.