Investment
Individuals invest when they find themselves with extra money and they want that money to work for them, meaning, increase in value. For instance, a person might make a certain amount of money each month at his job, but is able to spend less than he earns, therefore leaving some money over each month. A person can choose to set that money aside, either in a save place like a cookie jar, mattress or bank, and when he comes back after a year or so he will find he has exactly the same amount of money he put there. (Except in the case of the bank in which it is possible, in some places, to have less then you put there, due to bank fees and other expenses.)
Investments, on the other hand, allow you to come back after a certain amount of time and actually have more money than what you put there. This cannot happen inside a cookie jar, but can only happen when the company or person you give your money to actually make something or offers a service that goes up in value. On the other hand, there is no chance that when you come back to the cookie jar you will have less money, but with investments there is always that chance. The usual rule of thumb is that the more money you stand to make through investing, the larger the risk you are taking.
Investments are the fuel that runs healthy capitalistic economies. Lowering taxes usually increases investments, as there is more discretionary income available to work for you.
