| 1. | an alien who has legally established residence in the U.S. |
| 2. | an alien who has legally entered the U.S. as an immigrant with the intention of becoming a citizen. |
Resident Alien
A foreigner who is a permanent resident of the country he or she resides, but does not have citizenship.
Investopedia Commentary
Resident and non-resident aliens have different filing advantages and disadvantages. For example, a resident alien can use foreign tax credits, whereas a non-resident cannot. But on the other hand, a non-resident alien pays very little US tax on their income earned outside the US.
See also: Alien, Non-Resident Alien