Ghost orders, also known as "flash orders" or "flicker orders," refer to a trading practice where orders are placed and immediately canceled, creating a false market signal. This can be done to:

1. _Manipulate prices_: Creating a false sense of demand or supply to influence prices.

2. _Disrupt market activity_: Interfering with other traders' orders or market operations.

3. _Create market confusion_: Generating false market signals to confuse or mislead other traders.

Ghost orders can be harmful because they:

1. _Distort market prices_: Artificially inflating or deflating prices.

2. _Undermine market trust_: Eroding confidence in the market and its participants.

3. _Disadvantage other traders_: Unfairly impacting traders who rely on accurate market signals.

Regulators and exchanges have implemented measures to prevent and detect ghost orders, including:

1. _Trade surveillance_: Monitoring trading activity for suspicious patterns.

2. _Order book analysis_: Reviewing order book data to identify potential ghost orders.

3. _Cancellation rules_: Limiting the frequency or volume of order cancellations.

4. _Penalties and fines_: Imposing penalties on traders or firms engaging in ghost orders.

By addressing ghost orders, regulators aim to maintain a fair, transparent, and orderly market environment.