Katarche is a Greek term that was used in Hellenistic astrology to refer to the beginning or inception of an event or undertaking, particularly within the context of inceptional astrology.
The word katarche means “beginning”, “inception”, or “commencement”.
Astrologers seem to have used the term was to refer to the most symbolically significant moment in the start of a new venture, event or undertaking. An inception chart would then be cast for this moment, under the premise that the chart would depict both the nature and the future of whatever was begun at that moment in time. This was tied to the practice of what later became known as electional astrology.