Final answer:
Marking the close violation is an illegal activity aimed at manipulating a stock's closing price by executing orders at the end of the trading day.
Step-by-step explanation:
Marking the close violation refers to an illegal activity where a trader attempts to influence the price of a stock by executing buy or sell orders at the end of the trading day to affect the stock's closing price. This practice is considered a form of market manipulation as it can mislead investors and affect investment decisions.
Regulatory bodies like the Securities and Exchange Commission (SEC) in the United States monitor and enforce penalties against such violations to protect the integrity of the financial markets.