As Investors use of the term the amount of money income brought in from the use of principal. This can be composed of dividends, realized capital appreciation, royalties, and interest.  Yield may arise from rents of real estate or from personal property, including invested personal property, bonds, stocks, and investments of all kinds. 
Interest, dividends, and capital appreciation are earned by the original corpus, usually purchasing power in the form of money made available for investment, by the investor.
Yield from, to pay, to be worth, to repay, return, to cost, be worth, to be worth. c.1300 repay, return, render, produce, surrender. Earliest Eng. sense survives in financial "yield from investments. Payment, sum of money.