Spoofing
Also called: layering, spoof orders
Spoofing places large orders with no intention of executing them, to create a false impression of supply or demand, then cancels once the price moves. It became explicitly illegal in the US under Dodd-Frank and has produced criminal convictions, including of a trader whose home-based spoofing was linked to the 2010 flash crash. It's detected through cancellation rates rather than through individual orders.