Mission statement

A mission statement tells the purpose of a company or organization. Basically, it says in a very short way WHO the organization does something for, WHAT is the kind of thing it does, and WHICH WAY it does it (that is, instead of other ways one could do that same thing). It can be used to tell quickly what the organization does. It can also help to give members of the organization a common idea of what they're here to do. 
A mission statement basically sums up everything that something is about. Put very simply, for performance it would sum up what the purpose of the performance is. That might be to entertain.
Examples:
McDonald's - Mission statement: "To provide the fast food customer food prepared in the same high-quality manner world-wide that is tasty, reasonably-priced &amp; delivered consistently in a low-key décor and friendly atmosphere." 
World Vision - Mission statement (well, part of it): "...working with the poor and oppressed to promote human transformation, seek justice and bear witness to the good news of the Kingdom of God"