There are different types of plagiarism: Complete plagiarism, near complete plagiarism, patchwork plagiarism, lazy plagiarism and even self-plagiarism. Referring to Wikipedia, the definition of plagiasm is:
Plagiarism is the "wrongful appropriation" and "stealing and publication" of another author's "language, thoughts, ideas, or expressions" and the representation of them as one's own original work.
Plagiarism is considered academic dishonesty and a breach of journalistic ethics. It is subject to sanctions like penalties, suspension, and even expulsion. Recently, cases of "extreme plagiarism" have been identified in academia. The modern concept of plagiarism as immoral and originality as an ideal emerged in Europe in the 18th century, particularly with the Romantic movement.Here's a great blog dedicated to the problem of detecting plagiarism https://plagtools.com/ , I highly recommend reading it.
Plagiarism means to copy something and using it as your own. Cheating could be another word for Plagiarism.