The nominative case is a grammatical term used to indicate the subject of a sentence. In English, the subject is typically the person or thing performing the action of the verb. For example, in the sentence "The cat sleeps," the word "cat" is in the nominative case because it is the subject doing the sleeping. In many languages, including Latin and German, the nominative case has specific endings or forms that change based on the subject's gender or number. Understanding the nominative case is essential for constructing clear and correct sentences, as it helps identify who or what is performing the action.