The shares of stock that a corporation has issued and not reacquired are described as its outstanding shares. Some of but not all these shares are available for trading in the marketplace.
A corporation's market capitalization is figured by multiplying its outstanding shares by the market price of one share. The number of outstanding shares is often used to derive much of the financial information that's provided on a per-share basis, such as earnings per share or sales per share.
However, some analysts prefer to use floating shares rather than outstanding shares in calculating market cap and various ratios.
Floating shares are the outstanding shares that are available for trading as opposed to those held by founding partners, in pension funds, employee stock ownership plans (ESOP), and similar programs.