The difference between bid and ask — the direct trading cost in market currency.
The spread is the difference between bid (the price you can sell at) and ask (the price you can buy at). It's the central cost component in forex and CFD trading: tight spreads save money, wide spreads pull every trade into the red. EUR/USD typically has 0.1–0.5 pip spread at top brokers; exotic pairs like USD/TRY can be 30 pip or more. Suna AI Vision skips setups with spread above 2 pip in backtests and live filters — otherwise the spread eats the risk-reward.
EUR/USD bid 1.0850, ask 1.0851 = 1 pip spread. On a 1-lot long trade that's already 10 USD of cost at entry.