A complete thought is a sentence that contains both a subject and a verb. When a group of words forms a complete thought, it is known as an independent clause because it can stand on its own.
According to the DYC Learning Center, if a group of words does not contain the two elements that form an independent clause, a subject and verb, it is not a complete thought. Instead, it is a sentence fragment that is not grammatically correct. Typically, a complete thought can be verified if the sentence makes sense and the subject and verb can both be identified.