Cashflow Quadrant By Robert. T. Kiyosaki, Business Finance

Growing up, Kiyosaki's well-educated father recommended he aim for the E or S quadrants. But his father, who spent his life in these quadrants, was always relatively poor. On the other hand, Kiyosaki's best friend had a father who was a high school dropout but made it into the B and I quadrants and was wealthy. It was this "rich dad" who explained the Cashflow Quadrant.
At its simplest, the Cashflow Quadrant is a way to categorize people based on where their money comes from: E, S, B, or I.
E stands for an Employee, someone who earns money by holding a job. S is Self-employed, earning money for themselves. B stands for Business, meaning someone who owns a company or system that generates money for them. And I is an Investor, someone who earns money from their various investments.