Intentionally targeting civilians, or intentionally causing civilians to be targeted, with violence and threats instead of military targets.
The advantages of my definition:
1) Fits the common understanding of the word’s meaning.
2) Differentiates between collateral damage/casualties in an attack on a valid military target, and purposely targeting civilians.
3) Includes the use of human shields – the onus falls on those who hide behind civilians, not on those who accidentally hit the civilians while targeting the terrorist.
4) Can be applied to any side in a conflict (e.g. government or insurgent) as it does not take political factors into account, only means and methods.
5) Further to all of the above, accusations of terror acts can be objectively investigated (instead of the current practise of smearing your adversary as ‘terrorist’ as a first resort).
It is the difference between you visiting the bank and tragically getting killed in the crossfire of a police/robber-gang shootout, and the police and robbers intentionally aiming for you first and only continuing with their firefight once they’re sure you are dead.
Some might argue that using this definition automatically qualifies many ‘insurgents’ in Iraq, Afghanistan and Israel/Palestine while exempting the US, international and Israeli troops who fight them.