Ma'anar ƙamus na kalmar "cikakkiyar sifili" tana nufin mafi ƙarancin zafi mai yuwuwa, wanda shine ma'anar da dukkan abubuwa ba su da kuzarin zafi. Yawanci ana bayyana shi daidai -273.15 digiri Celsius (-459.67 digiri Fahrenheit) akan ma'aunin zafin jiki na Kelvin ko Rankine, bi da bi. A wannan zafin jiki, duk motsin kwayoyin halitta yana dainawa, kuma ana ɗaukar shi yanayin zafi mafi sanyi da zai iya wanzuwa a sararin samaniya.