By the definition of Part FCL, the Proficiency check means the demonstration of skill to revalidate or renew ratings or privileges, and including such oral examination as may be required.
It means, the proficiency check is the checkride with examiner to revalidate the rating - e.g. class rating or renew its validity once expired. The scope of proficiency check is allways the same.
It is important to note, that there is no proficiency check when it comes to instructor certificates. The proficiency check in this case is called assessment of competence.
Talking about the checkrides, there are generally two different kinds of proficiency check:
license proficiency check - associated with licensing (revalidation and renewal of the ratings) - also called as LPC
operator proficiency check - associated with checkrides within AOC holder (not applicable for licensing) - also called as OPC
There is no proficiency check for instructor's certificates.
Renewal (of, e.g. a rating or certificate) means the administrative action taken after a rating or certificate has lapsed for the purpose of renewing the privileges of the rating or certificate for a further specified period consequent upon the fulfilment of specified requirements.
Revalidation (of, e.g. a rating or certificate) means the administrative action taken within the period of validity of a rating or certificate which allows the holder to continue to exercise the privileges of a rating or certificate for a further specified period consequent upon the fulfilment of specified requirements.