A hanging man is a single-candle candlestick pattern which is just like a hammer, but which occurs in an uptrend to constitute a bearish reversal pattern. The hanging man looks like a hammer with a short body found at the upper end of a long shadow. Just like the hammer, the shadow must be at least twice as long as the body and the body must be found at the upper end of the shadow.
The hanging man is formed by a long shadow which represents a period of selling/profit taking following a rally, after which buyers came back stronger to push the price of the asset close to the open price. However, in many cases the inability of the buying strength to take the asset price beyond open price is a sign of impending weakness. If the next candlestick is bearish, it is a confirmation that the trend has changed to a bearish one.
The hanging man on its own is not enough to make a call that the trend has reversed in a bearish direction. There must be confirmation either by a bearish candle following the hanging man, or by an indicator that points to a bearish reversal. If the price has also hit resistance when the hanging man forms, this is a bearish confirmation as well.