Definition of 'Single Filer'
The filing status used by a taxpayer who is unmarried and does not qualify for any other filing status. Single filers include, according to The Internal Revenue Service (IRS), people who on the last day of the year are unmarried or are legally separated from a spouse under a divorce or separate maintenance decree, and he or she does not qualify for another filing status. Widow(er)s may be able to use the single filing status, but another filing status may prove to be more favorable. If more than one filing status applies to a taxpayer, he or she may choose the one that gives the lowest tax.
Investopedia explains 'Single Filer'
All persons who are required to file an income tax return with the Internal Revenue Service must choose a filing status. An individual can file under the five following statuses: single, married filing jointly, married filing separately, head of household, or qualifying widow(er) with dependent child.
Tax rates and standard deductions differ between the various filing statuses. Single filers can use IRS Form 1040EZ (if they have no dependent, are under age 65 and not blind, and meet other requirements), Form 1040A or Form 1040.