When a security's price falls in value over a given trading day and subsequently closes at a lower value than its opening price. A decline can happen for any number of reasons, including a reduction in the firm's intrinsic value, or as a result of the security's price dropping below its support level.






Taobiz explains Decline
Decline aggregate data is used to calculate the advance/decline index, which traders use to determine the direction of the market at any given point in time. It is often considered the most effective tool in gauging the market's direction or sentiment.