Title 26 Jurisdictional Statement on Income Tax

This is the IRS Jurisdictional statement detailing who is subject to Income Tax, and it refers to “citizens” or “residents” of the United States, the “the” jurisdiction thereof Congress/Federal Government United States.

What’s odd though is that it specifies that there’s some instances where a “nonresident alien” gets taxed too under 871(b) or 877(b). An “alien” is merely someone who is not a citizen or national of the United States per the U.S.C. If you read closer into these sections, they are about the taxation of expatriated citizens and the income of non-resident aliens who receive their income within the physical boundaries of the District of Columbia or earn income from Public Office.

https://www.ecfr.gov/current/title-26/chapter-I/subchapter-A/part-1/subject-groupECFR504ddca54174c57/section-1.1-1
CFR 26 1.1-1 Section 1 of the Code imposes an income tax on the income of every individual who is a citizen or resident of the United States and, to the extent provided by section 871(b) or 877(b), on the income of a nonresident alien individual.

National, National of the United States, Alien Code Definitions

https://uscode.house.gov/view.xhtml?req=(title:8%20section:1101%20edition:prelim)
Section 3: The term "alien" means any person not a citizen or national of the
United States.

But what does it mean to be a resident?