The "Server" term is used (capitalized) in the terminology section and throughout the document, but not defined. Note that OAuth 2 defines "Auhtorization Server" and "Resource Server" but not just "Server".
Drop Direct and Indirect Communication from the definition.
Make sure that which server we are talking about is clear (e.g., Authorization Server).
Make sure that defined terms are always capitalized, where defined terms are the ones that are defined in OAuth and OpenID specs.
Note: the term which is used as a normal word should not be capitalized.