Plagiarism
Presenting someone else's words, ideas, data, or structure as your own, whether deliberately or through careless citation.
Plagiarism is a claim of authorship you are not entitled to make. It covers copied text, unattributed paraphrase, borrowed argument structure, reused figures and data, and — in most institutions — buying or generating work and submitting it as yours.
Intent affects the penalty, not the definition. Most academic-misconduct cases are not deliberate theft; they are notes that lost track of what was quoted, a citation dropped in editing, or a paraphrase that stayed too close to the original.
The defences are procedural. Record the source and page as you take a note, mark quotations as quotations the moment you copy them, and cite when you use a source's idea even if none of its words survive.