in art and "outsider" is anyone who is creating work outside of the established dialogue of a certain field
so say I came to mu and posted a thread that consisted of nothing of charts detailing black on black crime statistics, I would be considered and outside poster
same thing with music. the irony of the outsider artist is that once they are recognized by those who are "in on the conversation", they effectively become part of it. like when kurt kobain reps daniel johnston and the shaggs, or when tim and eric put someone like david leibe hart on their show, those things essentially become part of a greater conversation surrounding popular culture and ultimately influence it in some way.