The money you gain or lose on your investments over a specific period of time.
Return on Investment (ROI) is a performance measure used to evaluate the efficiency of an investment, or compare the efficiency of a number of different investments.
For example, if you own a stock, you look at your returns on investment over a period of two years, and you may find that you have gains of $1,000. Is that good? Bad? Depends on what you're expecting from your returns, and what other investors have seen on their returns.
Example:
Put in a dollar. You expect to get more than a dollar back. If you invested a dollar and three years later you got back $3, your ROI was 300%. You made $2 in profits. But it's still written nomenclature as a return of 300%. If you invested $3 and 3 years later got back just $1, your return was -67%.