A harmonised standard is a European standard developed by a recognised European Standards Organisation. It is created following a request from the European Commission and is published in the Official Journal of the European Union (OJEU).
The use of these standards remains voluntary. Manufacturers, other economic operators, or conformity assessment bodies are free to choose another technical solution to demonstrate compliance with the mandatory legal requirements.
You can find the latest lists of references of harmonised standards published in the Official Journal of the European Union by following this link.