A subject marker is a grammatical element used in some languages to indicate the subject of a sentence. It helps clarify who or what is performing the action of the verb. For example, in languages like Korean and Tagalog, subject markers are attached to nouns to show their role in the sentence structure. In Tagalog, the subject marker "ang" is used to denote the subject, while "ng" indicates the object. This distinction helps speakers and listeners understand the relationships between different parts of a sentence, making communication clearer and more effective.