client和customer都可以指顾客、客户，有时会混用，因此，实践中也容易被混淆。但是有些场合是不能够替换的。

英英释义：

client：a person or organization using the services of a lawyer or other professional person or company.

customer：a person who buys goods or services from a shop or business.

区别：

client是指存在委托关系的客户，通常指我们通常所指的委托人或当事人。

customer通常指商业交易中所指的客户，亦即我们所说的消费者。

区分二者最简单的方法是client最终支付费用，获得的通常是“服务”(service);customer购买的通常是“有形商品”(goods)。

但是，法律英语中在表达“当事人、委托人”含义的时候，只能用client，不能用customer替换。 

例 Items subject to legal privilege (section 10 of PACE: These can never be seized and the definition follows the existing legal categories and includes communications between a solicitor and the client when giving legal advice together with the attendant documents, and communications and documents in connection with legal proceedings, such as reports and letters from experts.

【参考译文】享有法律特权的物件（ 证据法令第1 0 条）：这些物件是绝对不能被检取的，而它们的定义是根据现行的法律类别界定的，这包括在给予法律指导时律师及委托人之间的通讯和相关的文件，及有关法律诉讼的通讯和文件， 例如专家报告和信件。

例 If you fail to comply with any of your obligations and/or to meet your liabilities under any of the provisions of this Client Agreement including this Schedule, including without limitation failure to provide Margin, we may at our absolute discretion and without prior notice to you or your consent (a) decline to accept further Instructions in respect of Exchange Traded Options Business; (b) Close Out some or all of your Client Contacts with us...

【参考译文】假若贵方未有根据本客户协议及本附表履行本身的任何责任及/或偿还贵方的任何债务，包括未有提供保证金，则我方可无须事先通知贵方或获得贵方同意的情况下，采取绝对酌情权：(a)拒绝接受贵方在交易所交易的期权业务发出的进一步指示；(b)将贵方与我方之间的部分或全部客户合约平仓...

例 Revenue is reduced for estimated customer returns, rebates and other similar allowances and excludes value added tax or other sales related taxes.

【参考译文】收入指减去估计客户退货、回扣及其他类别津贴，并且不包括增值税或其他销售相关税项。 

例 Trade discounts may be used as a competitive stratagem to secure customer loyalty.

【参考译文】商业折扣可以用作保持顾客忠诚度的一种竞争策略。