According to the Delaware Instructions:
A Delaware Resident is an individual who is domiciled in Delaware for any part of the tax year or maintains an abode in Delaware and spends more than 183 days here.
A Delaware Part-Year Resident is an individual that moves into or out of Delaware during the tax year. You can choose to file the Part-Year return on the resident or nonresident form, whichever is more beneficial to you.
A Delaware Nonresident is an individual that did not reside in the state of Delaware at any time during the tax year.
If one spouse is a resident of Delaware and the other is not, you can file either a resident or nonresident return, whichever is more beneficial to you.
For more information, see Delaware Filing Requirements