Congress: Regular coming together on a representational basis of several hundreds - or even thousands - of individuals belonging to a single professional, cultural, religious or other group. A congress is often convened to discuss a particular subject. Contributions to the presentation and discussion of the subject matter come only from members of the organising body. Frequency: usually established in advance and can be either multiannual or annual. Most international or world congresses are of the former type while national congresses are more frequently held annually. A congress will often last several days and have several simultaneous sessions.