"Single Filing Status. Single filing status generally applies if you are not married, divorced or legally separated according to state law.
"Married Filing Jointly. A married couple may file a return together using the Married Filing Jointly status. If your spouse died during 2012, you usually may still file a joint return for that year.
"Married Filing Separately. If a married couple decides to file their returns separately, each person’s filing status would generally be Married Filing Separately.
"Head of Household. The Head of Household status generally applies if you are not married and have paid more than half the cost of maintaining a home for yourself and a qualifying person.
"Qualifying Widow(er) with Dependent Child. This status may apply if your spouse died during 2010 or 2011, you have a dependent child and you meet certain other conditions."
"Single Filing Status. Single filing status generally applies if you are not married, divorced or legally separated according to state law.
"Married Filing Jointly. A married couple may file a return together using the Married Filing Jointly status. If your spouse died during 2012, you usually may still file a joint return for that year.
"Married Filing Separately. If a married couple decides to file their returns separately, each person’s filing status would generally be Married Filing Separately.
"Head of Household. The Head of Household status generally applies if you are not married and have paid more than half the cost of maintaining a home for yourself and a qualifying person.
"Qualifying Widow(er) with Dependent Child. This status may apply if your spouse died during 2010 or 2011, you have a dependent child and you meet certain other conditions."
(Source: http://www.irs.gov/uac/Newsroom/Determining-Your-Correct-Filing-Status)