The difference between the highest price a buyer is willing to pay for a stock (the bid) and the lowest price a seller is willing accept (the ask). This gap represents the cost of trading and is where market makers make their profit. A wider spread typically means less trading activity or higher uncertainty about the stock's price.
If a stock has a bid price of $50 and an ask price of $50.10, the bid-ask spread is $0.10. When you buy the stock, you pay $50.10. When you immediately sell it, you get $50.00, losing $0.10 per share to the spread.
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