Plagiarism means using the exact words from another paper/author and NOT giving recognition (a citation/reference) to the original.
Based on this definition, NO plagiarism is allowed at all!!!
But you can report what another paper says and include a citation. If you use exact words from another paper you must use quotation marks and give the page number from which it came. This is NOT plagiarism.
Even if you reuse something from one of your OWN papers, you should reword it so the exact same words do not appear in two papers.
Thanks for your comments. i want to send my review paper in Elsevier. i am using 46 references in my bibliography and almost 80 citations. when i check my plagiarism level from turn it in, it was 10 % plagiarism because there are some numerical values so i detects but i use proper citation every where, so do u think 10% plagiarism is OK, can i submit my paper, Kindly reply me
Imran, you are making a common mistake, confusing similarity with plagiarism. In your explanation above, I think you are referring to similarity, possibly with a free or commercial plagiarism detection software. Thus, 10% similarity does not necessarily mean 10% plagiarism, because 10% of the text may simply be - by chance - similar to text somewhere out there in the literature, and thus similarity in such a case is 10%, but plagiarism is 0%. Very sadly, many editors confuse these concepts and reject manuscripts based on their ignorance!
Dr Jamie is right in explaining the difference between similarly and plagiarism. Many journals have no tolerance policy towards plagiarism. Some editors accept upto 10℅ in a document while others reject when it exceeds 5℅. It's always better to be careful.