First you need to understand the difference between such concepts as copyright protection and their protection. Copyright protection implies the establishment of the entire system of legal norms aimed at respecting the rights of authors and their successors. Copyright protection is a set of measures aimed at restoring and recognizing these rights in case of their violation.
A copyright infringement is an offense by which the use of works of science, literature and art protected by copyright is unauthorized by the author or copyright holder. It may also concern violations of the terms of the agreement on the use of such works. The most common copyright infringement is the illegal copying and distribution of works, as well as plagiarism.
Under copyright infringement is meant the illegal copying and distribution of copyrighted materials without the knowledge of the copyright holder. Such materials can be musical compositions, software, films, books, computer games. Possession of intellectual property rights is protected by the laws of most countries.
Copyright infringement can be such actions as: making copies, selling them, transferring to someone else, resale of legally acquired copies. Infringement of copyright is sometimes called plagiarism.
Infringement of property copyright is called counterfeiting or, colloquially, «piracy».
Under plagiarism is meant the intentional assignment of authorship of someone else’s work of science, thoughts, art or invention. Also, any violation of copyright law can be regarded as plagiarism. This may entail legal liability. On the other hand, in some areas that are not covered by any kind of intellectual property, plagiarism is possible. Such areas are mathematics and other fundamental sciences.