If you publish your own work then you are self-published. Whether your book is hand-engraved onto individual sheets of steel as was the original Book of Dave, or printed on paper in a more conventional book form, so long as you put it out there yourself and it bears the name of your own imprint on the copyright page it is self-published.
True self-publishing ensures that everything to do with the book remains firmly in the control of the writer. The self-published writer can, therefore, dictate his or her own jacket design, title, blurb and layout without interference, and instigate all sorts of innovative promotion plans without having to consult his publisher first. What seems to draw most people to self publishing, though, is the lure of keeping the bulk of the profits from the book for themselves. This does have the side-effect of turning the writer into a sales person rather than a writer, but some people are happy with that.
However: if the writer is not a talented designer or a meticulous editor, then the book is not going to be good. And regardless of how good the book is, if the writer has no sales expertise, and no sales platform for the book, then the book will not sell, and there will be no profits to be made.