Plagiarism is the act of plagiarizing which is when someone:
(Merriam-Webster Online Dictionary)
What is a citation?
A citation is a description of a book, article, website, etc. that provides enough information so that others can locate the source you used themselves. It allows you to credit the authors of the sources you use and clarify which ideas belong to you and which belong to other sources.
What information is included?
Citation information usually includes: author(s), date of publication, title, and publisher's name and location (and for articles: journal title, volume, issue and page numbers).