https://www.msn.com/en-ie/health/min...ime/ar-BBH6lY2
ICD (and in the US: DSM) are manuals that standardise the use of special medical and psychological terminology, listing criteria/symptoms that must be fulfilled to name the complex by a given diagnosis term. The intention was originally to make international research and science communication comparable, later interaction with health insuring companies became another big use (where it already started to derail, imo).