OCL is an open-source terminology management service designed to help organizations manage terminologies and metadata, improving the accuracy of data collection and reporting. It functions as an electronic reference for healthcare workers to access clinical codes and is a key component of eHealth architecture, enabling term lookup, validation, and transformation across information systems. Among its notable implementations are Ethiopia’s National Health Data Dictionary, PEPFAR’s Metadata Sharing Platform, WHO’s COVID-19 documentation resources, the OpenHIE Metadata Clearinghouse, and the Columbia International eHealth Laboratory Interface Terminology (CIEL). It primarily focuses on communicable diseases and other health areas.