Research ethics is the set of rules that keeps research honest and its participants safe: give credit where it is due, report what you actually found, and never treat people as mere data. The most tested rule is about credit: using another person's words or ideas without acknowledgement is plagiarism, even if you change some words.
Worked example: a student copies a paragraph, replaces every fifth word with a synonym, and submits it without citation. That is still plagiarism — mosaic plagiarism, also called patchwriting. Changing words does not create ownership; only genuine rewriting in your own structure, plus a citation, does.