The ask price, also called the offer, is the lowest price a seller in the order book is willing to accept right now. When you place a market buy order, it fills at the ask. The other side is the bid, the highest price a buyer will pay. The gap between them is the spread. Suppose SBI shows a bid of ₹800.05 and an ask of ₹800.10. A market buy fills at ₹800.10. The five paise difference looks tiny, but on 1,000 shares it is ₹50 on entry and again on exit, before brokerage. In thinly traded stocks the ask can be far above the bid, and a market order can fill at a surprising price. Checking the ask before buying, and using a limit order when the spread is wide, is a basic habit.