According to the Oregon instructions:
A Resident is someone who is domiciled in this state.
A Nonresident is someone who was domiciled outside Oregon and lived outside Oregon for the entire year.
A Part-Year Resident is someone who was domiciled in Oregon for part of the year. If you moved into Oregon, or moved out of Oregon to a different state during the tax year, you are considered a part-year resident.
What if I am a resident and my spouse is not?
If you are filing jointly and one spouse is a full-year Oregon resident and one is a part-year resident, you may file a joint part year return.
If you and your spouse are filing jointly and one (or both) of you is a nonresident, you may file a joint nonresident return.
What is a domicile?
Your domicile, is the place you consider to be your home and where you plan to return after an absence. Your domicile, is essentially your legal residence.