Selling before buying means that the first transaction is selling and then buying some or all of the foreign exchange in the account within the selling amount. The cumulative amount of foreign exchange in the buying account cannot be greater than that in the selling account. Selling account foreign exchange after selling first is called selling opening position, and buying account foreign exchange is called buying closing position.

Closing position refers to the behavior of futures traders to buy or sell futures contracts with the same variety, quantity and delivery month, but in the opposite direction, and to close their positions. Simply put, it means "sell what you bought and buy what you sold (short)."