OHLC is the alphabet of price action. Every candle, bar, and even line chart is ultimately built from four prices per time window: Open (the first traded price), High (the highest traded price), Low (the lowest), and Close (the last). On a candlestick chart these collapse into a body (open-to-close) and wicks (the high and low extremes). On a bar chart they collapse into a vertical line (high-to-low) with two horizontal ticks (open on the left, close on the right). On a line chart only the close is plotted.
Each of the four numbers carries a different weight in the trader''s mind. The open is the first vote — what participants thought was a fair price at the start of the period. The close is the consensus — what was agreed by the end. The high and low are the extremes — the levels that were tested but not held. Closes carry the most weight because they represent settled price; wicks (high/low) represent contested price; opens represent starting position.
OHLC also lets you compute volatility (high minus low), direction (close minus open), and conviction (where the close sits inside the range). A close near the high of the bar is more bullish than the same close in the middle; a close near the low is more bearish.
Bar charts and candlestick charts are visually different but informationally identical — same four numbers, different rendering. Candles are easier to read at a glance because the colour fills convey direction faster; bar charts are more compact and easier to layer with annotations. Most modern traders use candles, but understanding that the underlying data is OHLC keeps the conversation honest: nothing about a candle is special beyond how it visualises four prices.