ICD-9, or the International Classification of Diseases, Ninth Revision, is a coding system used to classify and code diagnoses, symptoms, and procedures. Developed by the World Health Organization (WHO), it was widely used in healthcare settings to facilitate the collection and analysis of health data, billing, and insurance claims. The ICD-9 system includes a comprehensive list of codes that represent various health conditions and treatments. It was replaced by ICD-10 in 2015, which offers more detailed classifications and improved coding options, enhancing the ability to track health trends and outcomes more effectively.