If some one publishes its own article with the same title and same subject matter in more than one journals, will this be considered as self plagiarism or not??
Peer-reviewed journals ask, as a condition of acceptance of a manuscript and the workflow involved in its review and administration, that an article hasn't been published elsewhere.
Self-plagiarism is the unacknowledged duplication of text from previously published work in another article that the author has written. It's no different from plagiarism -- it's just that the copied text was written by the author, not someone else.
Very occasionally, the same article may appear in different journals; the editor would have a strong reason for duplication. E.g. as a festschrift, or an anniversary of the original publication of a 'classic paper'. But would be an editorial decision, not a matter for an author.
Plagiarism by authors writing in biomedical publications is a concept that has been well defined for many years and consequently is well understood. It is acknowledged to be a pervasive problem as well as a significant ethical issue that plagues scientific writing and even erodes confidence in peer-reviewed publications.
Self-plagiarism, on the other hand, is still a murky area that remains subject to confusion and misunderstanding; thus, the way we see it, librarians can play a part in providing a clearer understanding of the topic.