Unintentional Plagiarism: Patchwriting
The first type of unintentional plagiarism is patchwriting which often occurs when students are attempting to paraphrase an author's idea.
Patchwriting happens when you rephrase a portion of an author's sentences but your language remains too close to the vocabulary and/or structure of the original text. Students can fall into patchwriting if they simply plug in their own synonyms while keeping the author's sentence structure.
This type of plagiarism can occur whether or not the original author is cited.
(From Rebecca Howard More "Plagiarism, Authorships, and the Academic Death Penalty" (1995); UM Beyond Plagiarism "Patchwriting as a Technique.")