Plagiarism is the most frequent academic integrity violation. It is a serious issue, because properly citing sources is an essential component of academic research and discourse. Original ideas or concepts are considered to be a person's property, and not crediting the contribution of others is seen as ethically wrong. If you do not cite a source, you do not acknowledge the creator's rights and contributions and are committing intellectual theft.
Quoting
Paraphrasing and Summarizing
Citing