The bomb blasts in Boston went off on April 15, the deadline for filing 2012 returns. However, in view of this event, the IRS has given affected taxpayers 3 additional months to timely file 2012 returns. There will be no penalties or interest on returns filed by July 15, 2013. Those who want more time to file can request an extension to October 15 as long as Form 4868 is submitted by July 15. However, interest still applies to unpaid tax balances (only the penalties and interest on timely filing have been waived, not the interest on timely tax payments).
The extension applies automatically to anyone living in Suffolk County, Massachusetts. Anyone else impacted by the event (e.g., an out-of-state runner) can request a similar extension by calling 866-562-5227 after April 23.
Source: http://services.taxanalysts.com/taxbase/tnt3.nsf/Current+Edition/4F67CD9A284A5E1D85257B5000099F5A?OpenDocument
A tax triggered if certain tax benefits reduce your regular income tax below the tax computed on Form 6251 for AMT purposes.