The thin line above or below a candle body showing how far price traveled beyond the open and close.
The parts of a candlestick. One candle sums up a slice of time: the thick real body runs from the opening price to the closing price, and the thin wicks reach out to the highest and lowest prices traded. Colour tells you which way the body ran.
Wicks show rejection. A long lower wick means price fell but buyers pushed it back up before the period closed. A long upper wick means sellers pushed it back down.
Wicks are where many stop-loss orders get hit and where stop-hunt talk comes from. Placing a stop just beyond a recent wick is common; so is getting stopped by the next one.
Example: a 5-minute candle on a stock opens at $30.00, spikes to $30.60, and closes at $30.05. The 55-cent upper wick shows the spike was sold immediately.