Islamic terrorism is a form of terrorism by those whose motivations are rooted in extremist interpretations of Islam.  Over 25% of terror-related attacks of violence in 2007 were caused by those self-identifying as "Islamic", according to the United States Government.
The Roots of Terror
According to the National Counterterrorism Center, the Islamic State of Iraq (aka al-Qa’ida in Iraq), more than any other subnational group, claimed they conducted attacks with the highest casualty totals. 
Qur'an Verses that endorse toerrorism