High price, in trading, is the highest price at which a security or contract changed hands during a stated period, such as a one-minute bar, a trading session, a week or the past 52 weeks. It is one of the four values in open, high, low and close (OHLC) data, alongside the opening price, the low price and the closing price, and it marks the top of the wick on a candlestick chart.
The high is taken from actual trades, not from quotes, so a single small trade can set it. Traders use session and multi-week highs as reference points: a prior high is often treated as a resistance level, and a move above it is the trigger in many breakout trading rules. The distance between the high and the low also feeds range-based volatility measures such as the Parkinson volatility estimator. Data vendors can differ slightly on a day's high, depending on how they treat off-exchange trades.