A big bearish candle has a body comprising over 70% of the day's range, with short wicks. Bears strongly dominated the session, closing well below the open with heavy selling pressure.
Bears fully controlled the market. After the open, bears took over and bulls couldn't mount a rebound. The close near the low, combined with heavy volume, shows large-scale distribution.
At trend peaks it's a topping signal; in a downtrend it's a continuation signal (win rate 71%). Enter short after close or at next day's open confirmation.
Confirm the location: at support, it may be a false breakdown; at resistance, it's a strong bearish confirmation.