In short. An iceberg order is a large limit order shown to the market in small slices: the DOM displays 20 contracts, they fill, 20 more appear at the same price, and so on until the hidden total is done. On the footprint it shows as a price where far more contracts trade than the book ever displayed; on a heatmap as a level that keeps refilling.
Icebergs matter because they are the mechanics of absorption: a passive participant who wants to buy 2,000 contracts without showing it. Detectors (DeepChartsOFF has one) compare the traded volume at a price with the displayed size and flag the excess.
A refilling bid that holds is support until it stops refilling; when the iceberg is done, price often moves fast through the level. Trade with the iceberg while it holds, with a stop a few ticks behind it, and get out when the refills stop.
Questions traders ask
What is Iceberg order?
An iceberg order is a large limit order shown to the market in small slices: the DOM displays 20 contracts, they fill, 20 more appear at the same price, and so on until the hidden total is done. On the footprint it shows as a price where far more contracts trade than the book ever displayed; on a heatmap as a level that keeps refilling.