What is a movement?

Our class discussion today left me thinking about the relationship or movements and individuals in definitions of terrorism. Discussing Hoffman today, we concluded that the individual needed to be involved in a movement in order to be defined as a terrorist. We also read from Hoffman who said that Sirhan Sirhan was not a terrorist because he was not linked to a movement. What then is a movement?
It appears to me that the movement as discussed in this definition must be organized. It does not seem to matter whether or not the individual is part of any organization seeking to forward the movement, as long as he has participated in the movement to an extent prior to the action that is classified as terrorism. An organized movement then is required for an act to be defined as terrorism. Again this led me to a question: What level of organization is needed and to what extent must one participate in the movement? I concluded that an ideology supported by an organization like Hamm as is obviously representative of an organized movement. I also concluded that the ideological movement that motivated Ted Kaczynski is definitely not an organized movement. The difference between the two movements is the development of institutions of some size with the express desire to forward the ideology. This definition also pushes me towards my previous question: to what extent must one participate in the movement to be a terrorist? Sirhan Sirhan was opposed to Israeli occupation of Palistine territories, a similar ideology to Hamm as, but is he not a terrorist because he didn't take physical part in the movement?
Sirhan Sirhan is as much a terrorist to me as any Hamm as member. He may not have been part of an organization, but he was a supporter of an organized movement. If he had even attended one meeting of such an organization, there would be little belief that he was not a terrorist. I do not see belonging to an organization in an organized movement as a prerequisite to being a terrorist. If you have a similar ideology and employ similar tactics to advance the similar ideology as part of an organized movement, then you qualify, at least on this one part of the debate, as a terrorist. I am not arguing that being part of an organized movement is a sufficient condition or a necessary condition, but I am arguing that Sirhan Sirhan was a terrorist contrary to the reading discussed today. I do not believe that you must be a member of an organization to be a terrorist, and that influence without direct contact is enough.