™A $49.90 bid and $50.10 ask have a $0.20 spread. Buying at the ask and immediately selling at the bid loses $0.20 per share before fees.
Orders & Market Structure
Bid-ask spread
The difference between the best displayed bid and ask prices.
Plain-English context
Put the definition to work.
Spread alone does not capture depth, price improvement, market impact or the spread cost already embedded in actual fills.
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