Definition problem

I don't like to see anyone killed by anyone else in anyway. I don't like fights, I don't like death sentences, I don't like wars, and I don't like terrorism.
I am sure that individuals/nations involved in any of the abovementioned acts can justify their purpose. However, I still don't understand the meaning of terrorism, and I can't analyze the justifications.

Terrorism:

1. Is it people killing people?
2. Is it soldiers killing soldiers?
3. Is it people killing soldiers?
4. or is it soldiers killing people?

This is what I think and is incomplete:
Number 1 is called FIGHT.
Number 2 is called WAR.
Number 3: I don't know, may be defence!
Number 4: This is what I hate the most and is probably what terrorism is all about.

What about the Israel-Palestine conflict?
What about Iran killing its dissidents?
What about Iraq bombing Kurds with chemicals during the Iran-Iraq war?

I raised the issue and I'll comment on it a little bit more later.