the astrodictionary definition:
 
Pars Fortuna. The Part of Fortune. One of the Arabian Points (q.v.). A point that bears the same relation to the Rising Degree that the Moon bears to the Sun. It occupies the same House-position in a Figure based on a birth-moment, that the Moon tenants in a Solar Figure. Its symbol, a cross within a circle ED, is that utilized by astronomers to represent the Earth. It is the ancient Chinese symbol Tien, a field; used by the Egyptians to signify territory. It is generally considered that the House position of Fortuna is an indication of the department of life that will most readily contribute to the financial welfare of the native. If so it tends to lend emphasis to the theory that one succeeds best at that which one likes best; that congeniality of occupation is a contributing factor to success therein. v. Arabian Points.