Any individual within the country’s borders, who is not a U.S. citizen, is called an alien.
The term ‘alien’ can be used in reference to any person within the country’s borders, who is not a U.S. citizen. Aliens are classified in two broad categories – non-resident aliens and resident aliens. According to the IRS, an alien who does not meet either of the substantial presence test and the green card test is known as non-resident. For instance, fresh arrivals in the country on F-1 or J-1 visa are usually non-resident aliens.
Individuals who meet either the substantial presence test (physical presence in the country for over 31 days in a year and 183 days in 3 years) or the green card test are called resident aliens. For more information on aliens and employers on immigration cases, please visit the Department of Labor (DOL) website.