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Type "Underpayment of Taxes" in the search box. 

When you don't have enough tax withholding and you don't make estimated tax payments during the year, then the IRS or your state can charge you with an underpayment penalty.  It is not the same as the interest or penalty the IRS will charge you for not paying your balance due on time (by April 15th).  

This penalty generally only applies when you owe more than $1,000 in federal tax on your tax return.  Basically, you get charged this penalty for owing too much tax and not making the proper payments during the year (either through withholding on your paycheck or estimated tax payments).