Include in your answer examples and references that allow for actions of the UK, US, French, Spanish, and Holy Roman Empires to not be called terrorism. Extra points will be granted if you can also discuss Palestinian independence and the creation of the State of Israel, the Mau Mau uprisings and the creation of the Country of Kenya, and the arrest and incarceration of Nelson Mandela for conspiring to commit acts of terrorism against the South African State. If time permits you may try to reach a satisfying narrative by concluding with the Good Friday agreement, and release of IRA/Sinn Fein members who were released despite being convicted of murder.
Terrorism is easy to define - violence by non-state actors that specifically targets non-military personnel for the purpose of causing political change. It is considered a civil crime rather than an act of war and those found captured in such acts do not receive the protections of the Geneva Convention.
It is separated from guerrilla warfare or even insurgency by the lack of a uniform, which is used to indicate the specific accountability of a government or organisation. Even an armband and locally designated rank is enough to require a captured combatant to be treated as a military prisoner, with all the protections and responsibilities conferred by international law.
The UK, US, French, Spanish and Holy Roman Empires were all nations. The responsibility for the actions of their armed forces fell originally to their monarchs, though as society has developed accountability now falls to the government of a nation state. Initial acts of the Palestinian intifada were undoubtedly terrorist, though the formation of HAMAS, with designated ranks and uniform, has made them into guerrilla fighters (many are still guilty of warcrimes for targeting civilians, but they cannot be considered genuine terrorists. Indeed, the universal military service in Israel makes even the idea of civilian targeting debatable).
If Nelson Mandela had planned to carry out a bombing campaign against uniformed targets while wearing the armband of an internationally declared armed force, he would have been planning a legitimate military campaign. By not doing so, he was planning a terrorist act. Early acts by the IRA, a declared and often uniformed insurgency, specifically target military and armed police, all of which are legitimate military targets. Early on, they could be considered guerrilla fighters. However, the civilian targeting by the Provos was an act of war.
Of course, it is the nature of civil wars, or wars of independence, that the ruling group label the insurgents as criminals rather than combatants, not least for the greater leeway it provides for extreme punishment. It was the retroactive negotiation of this status that led to the release of IRA members following the Good Friday Agreement.
Personally I agree with Tsoulasky - the deliberate targeting of civilians by non-accountable combatants for the purpose of political change is worthy of execution, as supported by the Geneva convention.
Sorry, Tsoulasky - I was a War Studies BA and couldn't help butting in.