Over the years, I have lost count of the number of 'vision' and 'strategy' meetings I have participated in, where we spent more of our time discussing the meaning of 'mission' and 'goals' and related words than we did actually considering the question in front of us.
A vision, if you want it to be useful, must be turned into reality - or, at least, have some sort of useful impact on reality. As well as a mission, any group needs to agree its priorities if it is to undertake any activities. All these things may be largely implicit, but it is helpful to make them explicit so that people don't make invalid or contradictory assumptions and then feel let down when the reality is not what they expected.
In keeping with the general ethos of this site, the document here is offered as a helpful framework - not to tell anyone what to do, or how to decide what you should be doing, but just a description of the things any group need to talk about, and perhaps a way to avoid endless arguments about defining terms.