What is the difference between widowed status and single
The single filing status is used if you are considered unmarried and you do not qualify for another filing status. Your filing status may be single if you were widowed before January 1, 2015, and didn't remarry before the end of 2015.
If your spouse died in 2015, you can use married filing jointly as your filing status for 2015 if you otherwise qualify to use that status.
The qualifying widow(er) filing status allows you to use joint return tax rates and the highest standard deduction amount (if you do not itemize deductions). However, you are not able to file a joint return.
You may be eligible to use qualifying widow(er) with dependent child as your filing status for 2 years following the year your spouse died. For example, if your spouse died in 2014, and you haven't remarried, you may be able to use this filing status for 2015 and 2016.