WHO IS A TERRORIST ?

What is the definition of a terror attack? Is it the faith of the attackers that matters the most to declare an strike as terror attack ? There is a tendency especially in the western countries to look at things this way. We have seen this in the case of Washington Naval Yard shooting. We have seen in this in the case of a devastating attack by an ultra nationalist on a youth convention in Norway. Whereas the Boston Marathon bombing was declared as terrorist attack within no time, though the casualties were less compare to the other ones I mentioned. Was it because of the faith of the suspected Tsarnaev brothers ? For the Western world the Washington and Oslo attackers were not terrorists despite the severity of their crimes and the devastation they brought. For them they were 'insane' and 'mentally ill'. Logically speaking whoever kills innocent people randomly is insane and mentally ill. Either you call all such fanatics as insane or declare all of them as terrorists. Shun this double standard NOW.