I do not think I have ever seen a definition or even a real discussion about a definition.
The term lacks meaning, a generic term applied to someone I, or anyone else would like to vilify; and, as you and I are not likely to get a lot of media attention, mainstream or otherwise, the term is used to promote ideologies of the person, people using it.
Here its not important that what is the real or accurate definition of terrorism but how it is justifiable, in specific context terrorist act must meet the criterion set out i.e, persistent, systematic and preplanned use of violence primarily used against civilians for killing of human beings and destruction of property in order to generate fear and achieve certain objectives or for securing supremacy of their ideology.