What is a 'sentence fragment'?

A sentence fragment is defined as a group of words that does not express a complete thought and often lacks either a subject, a verb, or both. This means that while it may contain phrases or clauses, it does not stand alone as a complete sentence that conveys a clear idea. For example, "Although she was tired" is a sentence fragment because it introduces a thought but doesn't complete it. To be considered a complete sentence, a statement must provide a full idea and ensure clarity, which is not the case with a fragment. Understanding this concept is essential in writing and communication, as sentence fragments can lead to confusion and ambiguity.