The official definition is any person who writes an article which is in the public domain can class themselves as published. This includes all the teenies who blog their views on line about fashion and pop trends.
My view is a harder but plainer concept to understand. I will class myself as published if I see a book of mine in print by a publisher other than me.
True, I do have the right to call myself 'published' as I have work in print in 3 or 4 anthologies, but to me the definition is not complete until I see my name on a book by another publisher.