Big traders can hide most of their buying or selling from the order book, and knowing this is useful for anyone reading market depth.

• An iceberg order shows only a tiny slice of its real size, and the hidden part refills the visible tip each time it fills.
• A trader wanting to buy a huge position can do it without telling everyone else what they are doing.
• This gets confused with spoofing, but it is not the same thing and it is fully legal.
• Spoofing is fake size placed to be seen and is illegal; an iceberg is real size placed to stay hidden.
• The dividing line is simple: faking an intention breaks the rules, concealing a real one does not.

Outlook: Order books will keep understating real demand and supply, so visible depth alone is a weak guide to where the big money sits.