Ask price

Ask is a price at which the base currency/asset is being sold on the market at the present moment, i.e. for a trader - the buying price. Buy trades open at the Ask price because you buy the base currency at the price offered on the market. Sell trades close at the Ask price because, when you close the Sell trade, you buy the base currency/asset (when you open a Sell trade, you are giving an order to your broker to buy a currency/asset now, taking responsibility to buy it from your broker later).