A subject is a specific area of knowledge or study that can be explored in various fields, such as science, literature, or history. In education, subjects are often categorized into core areas like mathematics and language arts, which help students develop essential skills and understanding. In the context of grammar, a subject refers to the part of a sentence that indicates who or what is performing the action. For example, in the sentence "The cat chased the mouse," the cat is the subject because it is the one doing the chasing.