What is terrorism?
Official definitions
"Terrorism''
means premeditated, politically motivated violence perpetrated against
noncombatant targets by subnational groups or clandestine agents
US Code, Title 22, Section 2656f. Annual country
reports on terrorism   
http://www.state.gov/s/ct/rls/crt/2006/82726.htm     
Terrorism is the use of force or violence against persons or property
... for purposes of intimidation, coercion, or ransom.  Acts of
terrorism include threats of terrorism; assassinations; kidnappings;
hijackings; bomb scares and bombings; cyber attacks (computer-based);
and the use of chemical, biological, nuclear and radiological weapons.
General Information About Terrorism   http://www.fema.gov/hazard/terrorism/info.shtm  
General discussion on
terrorism
For a discussion of definitions, and a 'consensus' that most (but not
all) people follow, see Tom O'Connor's class Terrorism: Understanding the Threat
  http://www.apsu.edu/oconnort/3400/default.htm
   Lecture one is about the definitions and types   http://www.apsu.edu/oconnort/3400/3400lect01.htm  
Alternate definitions:
Has terrorism changed?
Why is terrorism more frequent in some
areas?
other interesting topics.....
Comments on above essays
Alternate viewpoint, e.g., saying, well, its not so clear, or maybe its
different, etc.