these are the Ascendant (ASC), Descendant (DSC), Midheaven (MC), and Innum Coeli (IC), referring to the cusps of the first, seventh, tenth, and fourth houses, respectively.
The basic cross of the birthchart formed by the horizon and the meridian, consisting of the ascendant/descendant (see separate entries) and the midheaven(MC)/nadir(IC) axes.
The four most important and powerful points of a chart as defined by the house system being used. The points are defined by where the planes of the horizon and the meridian cross the ecliptic. These crossing points are the ascendent, descendent, midheaven (or MH) and imum coeli (or IC). Planets that are near one of these angles is emphasized and more important in a chart because of this proximity. See also House.