A Certificate is a written or printed declaration of some fact.

Organisations issue certificates to acknowledge an achievement.    It is normally signed, and looks official.

A certificate can be precise in what it states, or it can be vague.

It may state that you obtained 68% in an exam on module 5b of the advanced piano tuners course from the Society of Piano Tuners on the 15th August 2002.

Or it may simply state that the Society thinks you are a competent piano tuner.

So certificates should be interpreted with care.    If you have to pass an exam to join an organisation, their membership certificate vouchsafes some level of competence.    But if membership is open to all it does not.

Membership of a Chartered Institute implies a level of proficiency;   that of a local natural history society only an interest in the subject.

Membership certificates are one common type.

A completion certificate is another.    This acknowledges that the learner has completed a course, but says nothing about what has been learned, or what level the learner has reached, normally because no formal assessment has taken place.

Other certificates may acknowledge a level of competence which has been demonstrated to the satisfaction of the issuing body, through some examination or assessment process.

But a certificate, even one which acknowledges a level of professional competence, does not necessarily imply a right to practice, or constitute a licence in itself.

Diploma, like certificate, does not necessarily indicate a particular level of qualification.

Providers who offer both certificates and diplomas would normally regard the diploma as the higher award, but there are no regulations which require them to do so.

Nor is there any commonly-agreed understanding of the level that a diploma might recognise.

What matters is not what the qualification is called, but whether it is widely recognised by employers, professional bodies, and others.    And that may depend more on the content of the course than the qualification at the end of it.

For example, if you want to become a counsellor, accredited by the British Association for Counselling & Psychotherapy (BACP), they will only accept a diploma if the course included a supervised placement within it.