Overdiagnosis is a growing area of concern within patient safety. The associated overtreatment that results from overdiagnosis can lead to increased financial stress and harm for patients. Although prior research has shown that breast cancer screening may identify lesions that are not clinically meaningful and may lead to unnecessary testing and procedures, explaining the concept of overdiagnosis to patients and providers remains challenging. In this paper, the authors support the United States Preventive Services Task Force cancer screening guidelines and propose a standard definition of overdiagnosis as it relates to cancer screening—the detection of cancer through screening that would not have been otherwise diagnosed in a person's lifetime had screening not taken place. A past PSNet perspective highlighted overuse as a patient safety problem.