In 1988 services moved ahead of manufacturing as the main product of the United States economy. But what is meant by “services”? Some economists define a service as something that is produced and consumed simultaneously, for example, a haircut. The broader, classical definition is that a service is an intangible something that cannot be touched or stored. Yet electric utilities can store energy, and computer programmers save information electronically. Thus, the classical definition is hard to sustain.
The United States government’s definition is more practical: services are the residual category that includes everything that is not agriculture or industry. Under this definition, services include activities as diverse as engineering and driving a bus. However, besides lacking a strong conceptual framework, this definition falls to recognize the distinction between service industries and service occupations. It categorizes workers based on their company’s final product rather than on the actual work the employees perform. Thus, the many service workers employed by manufacturers—bookkeepers or janitors, for example—would fall under the industrial rather than the services category. Such ambiguities reveal the arbitrariness of this definition and suggest that, although practical for government purposes, it does not accurately reflect the composition of the current United States economy.
1988年，服务业超过制造业成为美国经济的首要产业。但是“服务”是指什么?一些经济学家把服务定义成生产和消费同时进行的行为，例如理发。更宽泛些，服务传统上是指无形的，摸不着的，不能储存的东西。可是电力设施可以储存能量，电脑程序可以保存电子信息。所以传统上的定义很难成立。
美国政府下的定义要更实际些。服务业是指除农业和工业外的其它所有行业。但是这个定义除了缺少概念上的结构，还无法区分服务性产业和服务性职业的差别。这个定义以雇员所在公司的最终产品为标准将雇员分类，而不是以雇员的实际工作为标准。这样，那些在工厂从事服务业的雇员(如图书管理员，门卫)就会被划分到工业类而不是服务业。 由此表明，这一定义不仅模棱两可、主观武断，还不能真实地反映美国当今的经济结构，尽管它对于政府目的而言是实际可行的。
