1. 卖者;销售者;销售商
A seller of a type of thing is a person or company that sells that type of thing.
e.g. ...a flower seller.
卖花人
e.g. ...Kraft, the largest seller of cheese in the United States.
卡夫公司，美国最大的奶酪销售商
2. (交易的)卖方
In a business deal, the seller is the person who is selling something to someone else.
e.g. In theory, the buyer could ask the seller to have a test carried out...
理论上，买方可以要求卖方进行一次测试。
e.g. Housing became a seller's market, and prices zoomed up.
房地产市场成了卖方市场，价格一路飙升。
3. (畅销或滞销的)商品
If you describe a product as, for example, a big seller, you mean that large numbers of it are being sold.
e.g. The gift shop's biggest seller is a photo of Nixon meeting Presley.
这家礼品店最畅销的商品是尼克松会见猫王普雷斯利的照片。