I think Palestine should have the right to defend themselves if attacked. However if they attacked first, then they know the consequences of attacking a neighbor. If they are not attacking then no country has a right to attack them without repercussions. So Palestine's response is not terrorism if they were attacked first.
The Palestinians are terrorists, so of course whatever acts they commit against Israel should be considered as terrorism. I know it's currently fashionable to see anything Israel does as aggression instead of self defense, but so far there is no proof that they have done anything to Palestinians that the Palestinians didn't start.
I do not believe Palestinian responses to Israeli aggression should be considered terrorism. If we continue to identify everything as terrorism the term will lose its meaning and have no real implications outside of the current terms we use for strikes, so I do not believe it is fair to call this terrorism.
All revolutionaries were terrorists right up until they take control. Then they are recognized as revolutionaries or some other positively spun word. Those that fought in the revolutionary war in the US were considered terrorists during the war. They had a different name for it, but thats what they were. When they won, the name changed because the right to tell the history is that of the victors.
Anyone who is oppressed and feels themselves to be under threat needs to be able to retaliate. That in itself is not terrorism. So, and perhaps this is in question, if the Israeli aggression came first then the Palestinians were entitled to respond in kind and they can not and should not be called terrorists.