Plenary session is a term often used in conferences to define the part of the conference when all members of all parties are to attend.
These sessions may contain a broad range of content from keynotes to panel discussions and are not necessarily related to a specific style of delivery.
The term has been used in the teaching profession to describe when information is summarized. This often encourages class participation.
The Congress of Vienna is an example of a "congress" that did not meet in plenary sessions.