Investopedia中对于nonresident alien 这一术语的定义如下：

A nonresident alien is a classification assigned to a non-U.S. citizen, or foreign national, who doesn't pass the green card test or the substantial presence test. If a non-citizen currently has a green card or has had a green card in the past calendar year, he or she would pass the green card test and would be classified as a resident alien.If the individual has resided in the U.S. for more than 31 days in the current year and has resided in the U.S. for more than 183 days over a three-year period, including the current year, he or she would pass the substantial presence test and also be classified as a resident alien.

Resident aliens are taxed on all earned income as if they were U.S. citizens, but a nonresident alien is subject to taxation only under specific circumstances. For a nonresident alien, only income that is generated from U.S. sources, excluding certain investments, is subject to taxation.

For example, if you live in England and own a company that operates in the U.S., but you have not been to the U.S. for five years and don't have a green card, the income generated by the business will be subject to U.S. tax based on the applicable nonresident alien status. Additionally, dividends from U.S. based corporations are taxed at 30% for every nonresident alien, while capital gains are not subject to U.S. tax.

根据以上内容可知，在美国的外国人分为resident alien和nonresident alien，其中resident alien是指拿到绿卡或者一年中在美国居住超过31天或者三年中在美国居住超过183天的外国人；resident alien交税视同美国公民交税，而nonresident alien只有对美国来源的收入交税，其中美国公司的投资收益是交30%的税，而资本利得不归美国税法管。

究其翻译，nonresident可以理解为：非居民/非常住的，alien可以理解为外国人，那nonresident alien这个词组就可以翻译为非居民外国人。