From the Latin, literally bottom of the heavens; the zodiacal point opposite the Medium Coeli (Midheaven, MC). The Imum Coeli is one of the angles and forms the fourth house cusp in an unequal house system. Abbreviated IC.
In astrology, the Imum Coeli (Latin for "bottom of the sky"), IC, is the point in space where the ecliptic crosses the meridian in the north, exactly opposite the Midheaven. It marks the fourth house cusp in most house systems (this is reversed in the southern hemisphere).