According to the documentation there is a ConferenceType type. It has the following possible values:
* CM_CONFERENCE / CM
* SCOPIA_CONFERENCE / Scopia

What does "CM" and "Scopia" mean? And how is this used?

CM is the standard accroynm for Avaya Aura Communication Manager.
Scopia is an outdated name for the Radvision product Avaya acquired that hosts multi party video conferencing.

As to how they are used, I infer they relate to what product is hosting the conference, however you will have to await someone who has more product expertise for a definitive answer.

Do you mean that

- "CM" is the same as "Adhoc Conference"?
- "Scopia" is the same as "Meetme Conference"?

as described on https://www.devconnectprogram.com/site/global/products_resources/avaya_client_sdk/programming_docs/current/javascript/communication/tech/developing_conf_app.gsp

From the perspective of the Client SDK, yes.
Unfortunately, there are only so many words in the English language that can be used to communicate concepts with. And I agree it would be best if the documentation for a SDK sticks to one term for a concept throughout the documentation package, but often when multiple people create and maintain the content that is not adhered to consistently. Communication Manager can be configured to support meet-me voice conferences; however the Client SDK does not integrate with the meet-me capability available with Communication Manager.

Yes, CM is a server that supports conferencing in an ad hoc style. Scopia is a conferencing server that supports conferencing in a meet me style.

This type is used internally to the SDK. It isn't exposed via a supported API for the client to use.