Spoofing
Spoofing is placing large orders you never mean to fill, to make the order book look heavier on one side, and cancelling them before price gets there. It is illegal on regulated stock and futures exchanges.
A spoofed order looks like any other wall. The only sign is what happens as price gets close: the size disappears instead of trading. That is why a wall tells you what is waiting now, not what will still be there when price arrives.
Learn more: practice: read your first order book.