Implementing rules are Commission regulations. A regulation is usually composed of a short introductory regulation, colloquially known as ‘cover regulation’, and Annexes thereto, containing the technical requirements for implementation. In the EASA system, these Annexes are usually called Parts (e.g. Part-21 is an annex to Regulation 1702/2003; Part-ORO is an annex to Regulation (EU) No 965/2012).
The ‘cover’ regulation is usually short (a few pages) and it includes:
Reference: https://www.easa.europa.eu/en/faq/18998