The 'Bid' is the buyer's price. It is this price that you need to know when you have to sell a stock. Bid is the rate/price at which there is a ready buyer for the stock, which you intend to sell.
The 'Ask' (or offer) is what you need to know when you're buying i.e. this is the rate/ price at which there is seller ready to sell his stock. The seller will sell his stock if he gets the quoted "Ask' price.
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