Just to clarify and muddy things at the same time
First there is no globally agreed upon official definition of terrorism
Definitions
* Dictionary
terrorism –noun
1. the use of violence and threats to intimidate or coerce, esp. for political purposes.
2. the state of fear and submission produced by terrorism or terrorization.
3. a terroristic method of governing or of resisting a government.
* United Nations
1. League of Nations Convention (1937): "All criminal acts directed against a State and intended or calculated to create a state of terror in the minds of particular persons or a group of persons or the general public".
2. UN Resolution language (1999):"1. Strongly condemns all acts, methods and practices of terrorism as criminal and unjustifiable, wherever and by whomsoever committed; 2. Reiterates that criminal acts intended or calculated to provoke a state of terror in the general public, a group of persons or particular persons for political purposes are in any circumstance unjustifiable, whatever the considerations of a political, philosophical, ideological, racial, ethnic, religious or other nature that may be invoked to justify them". (GA Res. 51/210 Measures to eliminate international terrorism)
3. Short legal definition proposed by Alex P. Schmid to United Nations Crime Branch (1992): Act of Terrorism = Peacetime Equivalent of War Crime
4. Academic Consensus Definition: "Terrorism is an anxiety-inspiring method of repeated violent action, employed by (semi-) clandestine individual, group or state actors, for idiosyncratic, criminal or political reasons, whereby - in contrast to assassination - the direct targets of violence are not the main targets. The immediate human victims of violence are generally chosen randomly (targets of opportunity) or selectively (representative or symbolic targets) from a target population, and serve as message generators. Threat- and violence-based communication processes between terrorist (organization), (imperilled) victims, and main targets are used to manipulate the main target (audience(s)), turning it into a target of terror, a target of demands, or a target of attention, depending on whether intimidation, coercion, or propaganda is primarily sought" (Schmid, 1988).[9]
United Nations Security Council Resolution 1373 discusses terrorism and is a primary UN authority for terrorism because it was issued under Chapter VII UN authority.
Resolution 1566 gives a definition:
criminal acts, including against civilians, committed with the intent to cause death or serious bodily injury, or taking of hostages, with the purpose to provoke a state of terror in the general public or in a group of persons or particular persons, intimidate a population or compel a government or an international organization to do or to abstain from doing any act.
—UN Security Council Resolution 1566
On March 17, 2005, a UN panel described terrorism as any act "intended to cause death or serious bodily harm to civilians or non-combatants with the purpose of intimidating a population or compelling a government or an international organization to do or abstain from doing any act."
The General Assembly resolution 49/60,, titled "Measures to Eliminate International Terrorism," adopted on December 9, 1994, contains a provision describing terrorism:
“ Criminal acts intended or calculated to provoke a state of terror in the general public, a group of persons or particular persons for political purposes are in any circumstance unjustifiable, whatever the considerations of a political, philosophical, ideological, racial, ethnic, religious or any other nature that may be invoked to justify them. ”
According to Antonio Cassese, that provision "sets out an acceptable definition of terrorism."
Former Secretary-General Kofi Annan has stated that there are several Conventions on Terrorism by non-state actors. They a) define a particular type of terrorist violence as an offence under the convention, such as bombing, financing, etc...; b) require State Parties to penalise that activity in their domestic law; c) identify certain bases upon which the parties responsible are required to establish jurisdiction over the defined offence; d) create an obligation on the State in which a suspect is found to establish jurisdiction over the convention offence and to prosecute if the Party does not extradite pursuant to other provisions of the convention.
*European Union
The European Union employs a definition of terrorism for legal/official purposes which is set out in Art. 1 of the Framework Decision on Combating Terrorism (2002).[15] This provides that terrorist offences are certain criminal offences set out in a list comprised largely of serious offences against persons and property which;
"given their nature or context, may seriously damage a country or an international organisation where committed with the aim of: seriously intimidating a population; or unduly compelling a Government or international organisation to perform or abstain from performing any act; or seriously destabilising or destroying the fundamental political, constitutional, economic or social structures of a country or an international organisation."
*United States
The United States has defined terrorism under the Federal Criminal Code. Chapter 113B of Part I of Title 18 of the United States Code defines terrorism and lists the crimes associated with terrorism. In Section 2331 of Chapter 113b, terrorism is defined as:
…activities that involve violent… or life-threatening acts… that are a violation of the criminal laws of the United States or of any State and… appear to be intended (i) to intimidate or coerce a civilian population; (ii) to influence the policy of a government by intimidation or coercion; or (iii) to affect the conduct of a government by mass destruction, assassination, or kidnapping; and… (C) occur primarily within the territorial jurisdiction of the United States… [or]… (C) occur primarily outside the territorial jurisdiction of the United States…"
-U.S. Department of Defense Definition of Terrorism
The calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological.
-The FBI defines terrorism as:
The unlawful use of force or violence against persons or property to intimidate or coerce a Government, the civilian population, or any segment thereof, in furtherance of political or social objectives.
*United Kingdom
The United Kingdom defined acts of terrorism in the Terrorism Act 2000 as the use or threat of action where:
(a) the action falls within subsection (2),
(b) the use or threat is designed to influence the government or to intimidate the public or a section of the public and
(c) the use or threat is made for the purpose of advancing a political, religious or ideological cause.
(2) Action falls within this subsection if it
(a) involves serious violence against a person,
(b) involves serious damage to property,
(c) endangers a person’s life, other than that of the person committing the action,
(d) creates a serious risk to the health or safety of the public or a section of the public or
(e) is designed seriously to interfere with or seriously to disrupt an electronic system.
*Definition from the Arab Convention for the Suppression of Terrorism
Any act or threat of violence, whatever its motives or purposes, that occurs in the advancement of an individual or collective criminal agenda and seeking to sow panic among people, causing fear by harming them, or placing their lives, liberty or security in danger, or seeking to cause damage to the environment or to public or private installations or property or to occupying or seizing them, or seeking to jeopardize a national resources.
OK…now who who do we call a terrorist?