It is the reverse of a buy wall. It is a method for preventing the current price of a cryptocurrency to go above a set value. It is done by placing one or multiple big sell orders. When the rising price reaches a set threshold, the sell wall is executed at the threshold value, therefore, ensuring that the price will not go higher until all the sell orders are fully executed.
In cryptocurrency exchanges, trading is accomplished by using an order book. Buyers write in the book their asking prices (bids) and sellers write in the book their selling prices (ask). When one or multiple sellers place a substantial order at a set value, the price won’t go above such a value until all orders have been completed.
For example, a cryptocurrency currently trades at $11, several sellers place an order at $ 12. As soon as the value reaches $ 12. the sell wall kicks in and the price won’t go above $12 until all sell orders have been completed.
It is used by big investors (whales) to manipulate the market.