In a traditional publishing situation, a publisher is a person or organization typically unrelated to the author. This unrelated entity takes care of all the responsibilities of publishing a book like the selection of a manuscript, preparing it for printing, printing copies, marketing and distribution. In self-publishing, the author herself takes on the role of a publisher. Hence, she bears all the responsibilities of publishing her book, in return retaining the power to make independent decisions about the content and presentation of the book. For more info, check out our Self Publishing 101 article.