Plagiarism implies the appropriation of the authorship of a work, or part of it, such as a paragraph or a sentence, by not indicating the origin or citing the original source. It is an infringement of copyright, and an example of scientific malpractice.
Plagiarism is committed in different situations, for instance:
When we present another person's work, or part of it, as if it were our own. For example, any paragraphs taken from another work must be placed between quotation marks, indicating the source of origin; likewise, whenever another author is paraphrased or summarized, he or she must be presented as the author of the original ideas. Failure to do this means we are plagiarizing
Buying work from a third party and signing it as your own
Auto-plagiarism is when an author presents his or her previous works again as unpublished ideas or results