it means that you are not liable to Estimated tax payment. Here is the definition from the IRS
Estimated tax is the method used to pay tax on income that is not subject to withholding. This includes income from self-employment, interest, dividends, alimony, rent, gains from the sale of assets, prizes and awards. You also may have to pay estimated tax if the amount of income tax being withheld from your salary, pension, or other income is not enough.
Estimated tax is used to pay income tax and self-employment tax, as well as other taxes and amounts reported on your tax return. If you do not pay enough through withholding or estimated tax payments, you may be charged a penalty. If you do not pay enough by the due date of each payment period you may be charged a penalty even if you are due a refund when you file your tax return.
Who Does Not Have To Pay Estimated Tax
If you receive salaries and wages, you can avoid having to pay estimated tax by asking your employer to withhold more tax from your earnings. To do this, file a new Form W-4 (PDF) with your employer. There is a special line on Form W-4 for you to enter the additional amount you want your employer to withhold.
You do not have to pay estimated tax for the current year if you meet all three of the following conditions.
•You had no tax liability for the prior year
•You were a U.S. citizen or resident for the whole year
•Your prior tax year covered a 12 month period
You had no tax liability for the prior year if your total tax was zero or you did not have to file an income tax return. For additional information on how to figure your estimated tax, refer to Publication 505, Tax Withholding and Estimated Tax.
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Estimated-Taxes
