Which coding system describes the reason for patient visit or encounter?

The coding system used to describe the reason for a patient's visit or encounter is known as the International Classification of Diseases, 10th Revision, Clinical Modification (ICD-10-CM). ICD-10-CM is a medical classification system published by the World Health Organization (WHO) that contains diagnostic codes to classify diseases, injuries, and other health-related conditions. It is widely used in healthcare settings for various purposes, including reimbursement, quality measurement, and public health data analysis.