The term Top Losers refers to stocks that have seen the drop in price usually the highest percentage decline, over a certain period of time like today or this week or this month.
Not necessarily since a stock can be a Top Loser owing to recent news, investors selling their stocks to make a profit, or market sentiment. This can create possibilities to acquire the stock at a lower price, but you must investigate first.
Stock prices and volume change constantly when the market is open. The percentage change and ranking of the Top Losers fluctuate constantly, thus stocks are in and out of the list.