You have decided to borrow stock from your broker, sell it in the market, and then (you hope) replace the borrowed shares when the price drops in the future- This is an example of

There are 4 main types of investments:
Shares. 
Property. ...
Cash.
Fixed interest.

Often, people take investment to be about buying and selling shares only. You buy a stock or bond, with the hope that its value will increase over time. Although investing comes with the risk of losing money, should a stock or bond decrease in value, it also has the potential for greater returns than you'd receive by putting your money in a bank account. Thus the common clubbing of investment and share investing.