A transaction involving fewer shares than in a "round" lot, which for most stocks is 100 shares.

Operating Expenses

The ongoing annual fee associated with mutual funds. This fee, expressed as a percentage, is deducted automatically from the assets to compensate for expenses such as investment management, legal, printing and distribution.

Opinion Letter

A written statement issued by the National Office of the Internal Revenue Service (IRS) to a sponsoring organization to address the acceptability of the form and terminology of a master or prototype plan, as well as any related trust of custodial account documentation.

Overbought

A security, usually a stock , that has had a sharp rise, usually as a result of vigorous buying, making prices too high. This is the opposite of being oversold.

Oversold

A security, usually a stock (also sometimes a whole market), believed to have declined to an unreasonable level due to vigorous selling. This is the opposite of being overbought.

Over-the-Counter Market

A communications network through which trades of bonds, non-listed stocks, and other securities take place. Trading activity is overseen by the National Association of Securities Dealers (NASD).