A sentence is a grammatical concept, and the meaning of a sentence is often studied as the abstract, intrinsic property of the sentence itself in terms of predication. But if we think of a sentence as what people actually utter in the course of communication, it becomes an utterance, and it should be considered in the situation in which it is actually uttered (or used). So it is impossible to tell if “The dog is barking” is a sentence or an utterance. It can be either. It all depends on how we look at it and how we are going to analyze it. If we take it as a grammatical unit and consider it as a self-constrained unit in isolation from context, then we are treating it as a sentence. If we take it as something a speaker utters in a certain situation with a certain purpose, then we are treating it as an utterance. Therefore, while the meaning of a sentence is abstract, and decontextualized, that of an utterance is concrete and context-dependent. The meaning of an utterance is based on sentence meaning; it is the realization of the abstract meaning of a sentence in a real situation of communication, or simply in the context.