The term "grammatical mistakes" refers to errors made in using proper grammar and sentence structure. Grammar is a set of rules that dictate how words are arranged, combined, and used in sentences to convey clear and accurate meanings. When someone makes grammatical mistakes, it means they have not followed the correct grammatical rules while writing or speaking, leading to confusion or misunderstanding about what they intended to say. These errors can include things like subject-verb agreement problems, incorrect word order, improper use of punctuation, and other issues that affect the overall clarity and coherence of a piece of language.