Spread
The difference between the bid and the ask price at a broker. It is an immediate cost of entering a position — it matters a lot in scalping.
Definition
The spread is the difference between the bid and the ask price — an immediate cost of entering (and often exiting) at a broker. The thinner the liquidity or the higher the volatility (around news, for example), the wider the spread tends to be; on stocks and ETFs the depth of the order book matters as well.
Example
EUR/USD quoted at 1.0850 / 1.0852 has a spread of 0.2 pips. You buy at the ask of 1.0852 — you are immediately “under water” relative to the mid, before the price has moved in your direction at all.
Anti-example / common mistake
Comparing brokers on the marketing claim of “spreads from 0.0” instead of the typical spread during the hours you actually trade. On small GPW companies a “cheap price” with a wide spread turns out expensive once you complete a round turn.