Ghost authorship is when someone who substantially contributed to a study is left out of the author list. Gift authorship and guest authorship are when someone who doesn’t qualify as an author is still given credit for being one. (sumber)
Self-plagiarism is the same as regular plagiarism, however, the person whose content you are plagiarizing is you! Plagiarism is seen as theft, where you steal others’ intellectual/ creative/ academic property without giving them due credit. Self-plagiarism happens when you recycle or reuse parts of text from a paper you had submitted or published already. (sumber)