Capital input can also be called investment, or new investment. It is new money being invested in the business, not as loans or repayment of loans, but as money invested in ownership.
This is also money at risk. It will grow in value if the business prospers, and decline in value if the business declines. This is closely related to the concept of paid-in capital, on the balance sheet table. Paid-in capital is the amount of money actually invested in the business as money, checks written by investors. Paid-in capital increases only when there is new investment. It is different from retained earnings.