To answer we need a brief definition on the different forms of war. There is Conventional, Unconventional, and technically Terrorism (Although its not used often in most countries.) Conventional is where the two militaries will meet on the field and duke it out. Unconventional is where a inferior force will use guerilla warfare and hit-and-run tactics. Terrorism is the use of terror to influence something or to get what you want.
So how its different is that it usually is used by inferior forces, it is often used against the country itself or civilians. The terrorists will use suicide bombs and teams of armed fighters against the civilians to influence the leader of the country or to destroy morale. They want to get people so afraid that they will make peace or stop fighting in fear of more acts of terror.
One thing you have to keep in mind is that terrorism is not usually used just like this. Some people might use terrorism just for the sake of killing people. Or they might use it to reinforce their authority. Its not a hard and fast answer.
I hope this answers your question. If you would like more info or some examples I'll be happy to oblige.