A large limit order is placed at the desired cryptocurrency price to sell those coins when the price reaches the desired level.

When looking at a cryptocurrency exchange order book, you might come across sell walls and buy walls. A sell wall is a large order or group of orders to sell cryptocurrency at a certain price. These price levels are usually psychological ones or important ones in technical analysis.

Essentially, it is a group of traders who have identified a certain price as the lowest - or highest - they want to go with the price of their deserted coin before selling for a profit, or to mitigate further losses. The reason these sell walls are important to note is they often lead to a price drop when hit.

A mass sell-off of any asset floods the market with supply, lowers the demand, and thus drops the price. These sell walls can also cause panic selling by others, causing a snowball effect in the price drop.

Sell walls are also often seen as points of manipulation by whales, or large holders of a certain cryptocurrency. Sell walls can suppress asset prices and force them to be traded within a certain range. These also show other traders that the price won't go further from a level without passing significant resistance.

Sometimes, when intentionally done by whales, sell walls can be used as a bluff in manipulating the market. Often these sell walls are put up without any intention to buy from other traders at such levels, but they are wanting others to place their sell orders below the wall, which would, in turn, cause a downward price movement - ideal for shorting.

Sell walls can be made and broken down with ease by individual whales, but some are created naturally by groups of traders who have similar ideas on the price of a cryptocurrency. The opposite of a sell wall is a buy wall; similar in what it is, but different in execution and use. This is mostly there to cause upward price movements.