A spike is a sudden, sharp move in price, volume, or volatility over a short period. It often appears right after unexpected news, economic data, an earnings report, or a central bank announcement.
A price spike is a fast move up or down. A volume spike is trading activity jumping far above normal levels. A volatility spike is a sudden rise in the size of price swings. Spikes can come from a rush of orders hitting one side of the market, a cascade of triggered stop-loss orders, or a sudden drop in liquidity.
A spike is not a trend. A trend is a sustained move in one direction across many bars, while a spike is a single violent move that often reverses once the initial order flow clears. Because a spike can blow through resting orders, it is a common cause of slippage.
You are watching gold at USD 2,350 before a US inflation report.
The report lands higher than expected, and XAUUSD jumps to USD 2,375 within minutes:
2,375 - 2,350 = USD 25
That USD 25 move in minutes is a price spike, driven by the surprise in a major economic release.