What is volume?

Volume is the amount of trading that changed hands in a period — how many shares, contracts or coins were bought and sold. On a chart it usually appears as vertical bars beneath the price; each bar covers the same period as the candle above it. A tall bar means heavy participation, a short bar means thin participation.

What separates volume from price is this: price shows WHAT the market decided, volume shows HOW MANY participants stood behind that decision. Of two candles the same size, the high-volume one is a move endorsed by a crowd; the low-volume one is a picture produced by few participants, and easier to unwind.

Let us make clear from the start what volume does NOT say: volume has no direction. High volume does not mean "buyers won" or "sellers won" — every trade has both sides, so volume is always their combined activity. Direction comes from price; volume only measures the crowd behind that direction.