Dual Status Alien
What is a dual status alien?
A dual status alien is an individual who both meets the substantial presence test and either ends their U.S. tax residency or begins their U.S. tax residency in the same year. If they start their U.S. tax residency, then they must file a 1040 with a 1040NR attachment. They will file a 1040NR with a 1040 attachment if they are ending their U.S. tax residency. The 1040NR will only report U.S. sourced income for the nonresident period while the 1040 will report worldwide income for the resident period.
Note that green card holders in their first year may be dual status aliens. Also, a green card holder or U.S. citizen who expatriates is a dual status alien in their final year.