Caveat: this answer contains a moderately long, and perhaps subjective, description of the past actions of one group often described as terrorist, and a tangent on the current actions of a state. I don't intend to start a debate on the politics surrounding those actions here, but in order to make my point, it's necessary to go into a little more detail than would normally be the case in a Meta post.
This is a response to DVK's answer (I suspect it will be a little too long to add as a comment).
I see a problem with restricting the definition to actions which "deliberately target or disregard the safety of non-combatants (civilians)". In the second half of the 20th century, the most significant organisation involved in what most observers described as terrorist activity in the UK was the Provisional IRA.
The Provisional IRA has claimed throughout its existence that it is not a terrorist organization, using pretty much the same argument that DVK makes. Its targets have, in general, been:
What it sees as a military occupation of the north of Ireland, and
The infrastructure of what it sees as the occupying power, namely the United Kingdom.
Approximately one third of the casualties attributed to Provisional IRA actions have been civilians. However, the organisation made a point of issuing warnings prior to its attacks (at least, those on infrastructure targets), and claimed that these casualties were not intended (and that the UK was ultimately responsible for them). It would, therefore, claim that it neither deliberately targetted nor disregarded the safety of non-combatants.
Nevertheless, if you ask pretty much anyone in the UK mainland who lived through their campaign whether the Provisional IRA were engaged in terrorist activity, you'll get an emphatic "yes" in response, and an argument along the lines that their civilian casualties were unintended ... well, to be polite, it's unlikely to be well received in most quarters.
The problem is one of judging the honesty of declarations of intent. The IRA were fully aware that their actions were likely to cause significant civilian casualties, and as such, it's plausible to assert that those casualties were intended.
At the very least, a question along the lines of "Is the Provisional IRA a terrorist organization?" is a reasonable one, and one that cries out for the tag terrorism.
The example of the Provisional IRA is not, by any means, an isolated one. It would not be difficult to construct an argument that US drone strikes in Afghanistan and Pakistan amount to terrorist activity; while of course the US military will claim that the high level of civilian casualties caused by such attacks are unfortunate accidents (and likely make an "our opponents are ultimately responsible" argument analogous to that of the Provisional IRA), based on the evidence so far it would be absurd for them to claim that they are unaware of the likely consequences of those attacks.
A reasonable person, therefore, could argue that a party which takes an action in the full knowledge that said action will cause civilian casualties is responsible for those casualties, and that claiming they are unintended is at best irrelevant, and at worst mendacious.
In summary: it's complicated. Realistically, I don't think it's possible to give an objective definition of terrorism, or at least one which has a chance of reaching a consensus.
However, I stand by my previously-stated position that the terrorism tag is useful. Attempting to find synonyms smacks of bowdlerism to me, frankly, and the subject is one which is worth raising questions about (even if that means questions using the tag need to be moderated with more care than others).