What's the difference between a company's outstanding shares and its "float"? Well, all the shares a company has issued are its "shares outstanding." Company insiders may hold some of the shares, while the public owns the rest. Insider shares are usually held for a long time and are not traded too often, while shares in public hands trade more frequently. The shares owned by the public represent the "float."

Imagine Holy Karaoke, Inc. (ticker: HYMNS), which has 50 million shares outstanding. If the CEO and other insiders own 40% of them, then the float is the remaining 60%, or 30 million shares.

It's good to pay attention to this number when you're looking at smaller companies, since stocks with small floats (referred to as "thinly traded") can be extra volatile. Any demand will send the stock price soaring, since supply is so limited, and vice versa.