顾客或客户可以指用金钱或某种有价值的物品来换取接受财产、服务、产品或某种创意的自然人或公司 。是商业服务或产品的采购者，他们可能是最终的消费者、代理人或供应链内的中间人。

在市场学理论中，供应商必须营商事前，了解客户及其市场的供求需要，否则事后的「硬销」广告，只是一种资源的浪费，又不环保。

现代社会中，「顾客就是上帝」是企业界的流行口号。在客户服务中，有一种说法，「顾客永远是对的」。不过各方有不同的演译，例如顾客二字的个别定义。

顾客一词源于习惯。一个顾客是时常探访某店舖的人，他常在该处购买，和店东维持良好关系。

A customer (sometimes known as a client, buyer, or purchaser) is the recipient of a Good or a service, or a product, or an idea, obtained from a seller, vendor, or supplier via a financial transaction or exchange for money or some other valuable consideration. Etymologically, a client is someone merely inclined to do business, whereas a purchaser procures goods or services on occasion but a customer customarily or habitually engages in transactions. This distinction is merely historic. Today customers are generally categorized into two types: