What does the subject of a sentence refer to?

The subject of a sentence is fundamentally about who or what is performing the action. In a typical sentence structure, the subject usually comes before the verb and indicates the doer of the action. For example, in the sentence "The dog barks," "the dog" is the subject because it is performing the action of barking. Thus, understanding the subject as the one performing the action is crucial for sentence construction and comprehension.

The other aspects mentioned in the options—action, descriptor, and location—highlight other important components of sentence structure but do not directly define what the subject is. The action represents what is happening, descriptors provide additional information about the subject, and location gives context about where the action occurs. However, none of these elements define the subject itself, as the subject specifically identifies the actor of the action described by the verb.