Definition
A candlestick is a chart symbol that summarizes one period's opening, highest, lowest and closing prices. Its rectangular body spans the open to the close, and thin lines called wicks extend to the period's high and low.
How it works
Each candle summarizes one interval using its open, high, low and close (OHLC): the body spans open to close, and the wicks show how far price traveled beyond it. Colors are only a convention that varies by market and platform: HKEX quotation screens show rising prices in green and falling prices in red, while mainland China shows the reverse, so check the legend.
Long bodies suggest a decisive move, long wicks show rejection of an extreme, and small bodies show indecision. Named patterns such as the doji or hammer only describe shapes; their meaning depends on the time frame, the prior trend and the instrument.
Formula / convention
Body = abs(Close − Open); Upper wick = High − max(Open, Close); Lower wick = min(Open, Close) − Low
Illustrative example
Illustrative: a fictional share opens at HK$50.00, reaches HK$52.00, falls to HK$49.00 and closes at HK$51.50. The body is HK$1.50 (50.00 to 51.50), the upper wick is HK$0.50 (52.00 − 51.50), the lower wick is HK$1.00 (50.00 − 49.00), and the full high-low range is HK$3.00.
What to watch for
A single candle describes only what has already happened, and patterns carry no guaranteed predictive power; the same pattern can look different on different time frames. Test any pattern-based rule on historical data, including trading costs, before giving it weight.