According to the Wisconsin instructions:
A Resident is an individual that is domiciled in Wisconsin for the entire tax year.
A Nonresident is an individual that is not domiciled in Wisconsin at any time during the tax year.
A Part-Year Resident is an individual that is domiciled in Wisconsin for part of the tax year.
What if I am a resident and my spouse is not?
If one spouse is a resident and the other is not, file a nonresident joint return.
What is a domicile?
Your domicile is the permanent legal home you intend to use for an indefinite or unlimited period, and to which, when absent, you intend to return.
For more information: