In parliamentary procedure

Parliamentary procedure

Parliamentary procedure is the body of rules, ethics, and customs governing meetings and other operations of clubs, organizations, legislative bodies, and other deliberative assemblies...

, a session is a meeting or series of connected meetings devoted to a single order of business, program, agenda, or announced purpose.

Robert's Rules of Order Newly Revised (RONR)

An organization's bylaws may define a specific meaning and/or length of the term "session." The main significance of a session is that one session generally cannot tie the hands of a majority at a future session, except by adopting a special rule of order or an amendment to the bylaws, each of which require more than a majority vote. A session has implications for the renewability of motions. The same or substantially the same question cannot be brought up twice in the same session except by means of the motions that bring a question again before the assembly. However, RONR notes that "A previously considered motion may become a substantially different question through a significant change in the wording or because of a difference in the time or circumstances in which it is proposed, and such a motion may thus be in order when it could not otherwise be renewed."