Reinvestment is the move of putting that money back, or the money itself when it is put back. You use money you have earned from investments to buy more investments, instead of taking it out. Banks and share plans talk about dividend reinvestment: the cash your shares pay you is used, straight away, to buy more of the same shares. A company's reinvestment of profits is the choice to grow the business rather than hand the money to owners. Though actually, like the verb, the noun gets stretched in business talk to mean any putting of profit back into the firm. It is a money-page word, a little dry, and more at home in reports than in kitchen talk.