Junior Securities come last in the pecking order if a company gets liquidated; common stock shares are the most prevalent example.
Junior securities are securities such as common stock which would be the last in order to receive any payout if the company were to go bankrupt. Examples of securities which are senior are Preferred Stock and Bonds; senior securities receive service first in the event of company insolvency.
Interestingly, however, the owners of common stock have voting rights in the company, while the owners of senior securities, in most cases, do not. The owners of seniors securities are considered lenders in the case of bonds and preferred stock, while the owners of common stock are part owners in a company. This is why Shareholder’s Equity is also called Owner's Equity.