In business and finance, a share (also referred to as equity share) of stock means a share of ownership in a corporation (company). In the plural, stocks is often used as a synonym for shares especially in the United States, but it is less commonly used that way outside of North America.1

In the United Kingdom, South Africa, and Australia, stock can also refer to completely different financial instruments such as government bonds or, less commonly, to all kinds of marketable securities.2

Types of stock

Stock typically takes the form of shares of either common stock or preferred stock. As a unit of ownership, common stock typically carries voting rights that can be exercised in corporate decisions. Preferred stock differs from common stock in that it typically does not carry voting rights but is legally entitled to receive a certain level of dividend payments before any dividends can be issued to other shareholders."Stock Basics", Investor Guide.com.Zvi Bodie, Alex Kane, Alan J. Marcus, Investments, 7th Ed., p. 26–53. Convertible preferred stock is preferred stock that includes an option for the holder to convert the preferred shares into a fixed number of common shares, usually anytime after a predetermined date. Shares of such stock are called "convertible preferred shares" (or "convertible preference shares" in the UK)

Although there is a great deal of commonality between the stocks of different companies, each new equity issue can have legal clauses attached to it that make it dynamically different from the more general cases. Some shares of common stock may be issued without the typical voting rights being included, for instance, or some shares may have special rights unique to them and issued only to certain parties. Note that not all equity shares are the same.

Stock derivatives

A stock derivative is any financial instrument which has a value that is dependent on the price of the underlying stock. Futures and options are the main types of derivatives on stocks. The underlying security may be a stock index or an individual firm's stock, e.g. single-stock futures.

Stock futures are contracts where the buyer is long, i.e., takes on the obligation to buy on the contract maturity date, and the seller is short, i.e., takes on the obligation to sell. Stock index futures are generally not delivered in the usual manner, but by cash settlement.

A stock option is a class of option. Specifically, a call option is the right (not obligation) to buy stock in the future at a fixed price and a put option is the right (not obligation) to sell stock in the future at a fixed price. Thus, the value of a stock option changes in reaction to the underlying stock of which it is a derivative. The most popular method of valuing stock options is the Black Scholes model. Apart from call options granted to employees, most stock options are transferable.