The “qualifying widow(er)” filing status is for a person whose spouse has died and the surviving spouse is still raising kids.
In the year of the spouse’s death, the surviving spouse will file as married filing jointly. The surviving spouse can then file as a qualifying widow(er) in the next two tax years after that.
Example
Alex and Angie are married with two children. Alex dies in 2016, leaving Angie as a widow. Angie will file a 2016 tax return jointly with Alex, using the married filing jointly filing status. Angie can use the qualifying widow filing status for 2017 and 2018. She would then use head of household filing status for 2019 and beyond (for as long as she’s still raising kids).
(NOTE: If Angie remarries, she’d no longer qualify for qualifying widow filing status; instead, she’d file as married with her new spouse.)
The qualifying widow(er) filing status uses the same tax brackets and standard deduction amounts as the married filing jointly filing status.