"Gather in the stops" is a trading strategy used by investors to trigger stop orders already in place so that the price of the stocks trade higher or lower. This strategy involves selling or buying vast amounts of stock to either drive down or drive up the stock price.
"Stops" refers to stop orders. A stop order is an order to buy or sell a stock when it reaches a particular price. There are two types of stop orders: buy stop and sell stop. A sell stop is used to guard against losses and is usually referred to as a stop-loss order. A stop loss order goes into effect when the current stock price goes below the purchase price. For example, an investor can buy a stock at $30 and put in an order to sell if it goes below $28. A buy order goes into effect when an investor is involved in a short sale. If an investor is short selling, he or she may sell at $30 and put in a stop order to buy at $28.
When an investor "gathers in the stops", he or she usually has a specific goal in mind: to either cause a decline or increase in a particular stock price. When massive amounts of a particular stock are sold, the stock price goes down and the reverse is true if massive amounts of a stock are bought. So if an investor "gathers in the stops" by selling large quantities of stock, the stock price goes down, stop loss orders to sell are activated and the price of the stock declines further. If an investor gathers in the stops by buying stocks, the stock price increases, buy orders are triggered and the stock price ascends further.
To learn more, read The Stop-Loss Order - Make Sure You Use It.
This question was answered by Chizoba Morah.