The ancient Greek term "Symposion" (also Symposium) stands for "drinking together, drinking in company".
The translation of "banquet" led falsly to the common belief that a symposion was nothing more than a wassail. But for the ancient Greek the main point was something else:
the conjoint devotional and adequately ritualized sociality.
After dinner the guests would gather around the family altar. Then the Symposium would be initiated by cultic cleansing rituals such as washing hands and sprinkling the guests with fragrant essences. After that they would all put ivy, myrtle and flower crowns on themselves but also on the drinking vessels. Red and white woolen bandages were also in use. This was the way of manifesting the affiliation to the circle of the servants of Dionysos.
Each one of the round drank the first sip of wine out of a bowl that was supposed to be passed around, to honor the good spirit Daimon. As a sign of deifying the gods, wine was contributed to the gods, by throwing it out of the vessel. Flute music accompanied an old cultic song, that was sung to honor Apollon.
Afterwards some songs, the Skolia, were sung, that were dedicated to the Symposion. Mostly intellectual conversations might have followed, Xenophon also describes artistic presentations in the "Symposion". Speeches on a certain topic were improvized- q.v. Platon- riddles were solved , that were asked by each other, or they enjoyed the popular game of drawing accurate comparisons.
Very often one of the present guests was chosen to be the Symposiarch. He was the one, who defined the details for the drinking fiest and the topics and who took care that a certain adequat order was kept. It was expected from an honorable man, not to forget his virtue, over drinking, and furthermore, to find his way home without company as well.
The only written rules for celebrating the Symposion, that still exist today, are the ones in Platon's Nomoi. A poem with the same name, by Xenophanes of Colophon witnesses, that the celebration of the Symposion existed already in the 6th century BC. The celebrations as here described, existed until the end of antiquity.
In the Christian tradition the Symposion is also understood as a eucharistical society at the Last supper; the adequat archetype might be the "Feeding of the Five thousand" in the Gospel of Marc (Mk 6,39f)
The today's used term of the Symposion reflects the meaning only fragmentarily.