Douglas Harper's Etymology Dictionary
Wikipedia
A (German for "regulars' table", ) is an informal group meeting held on a regular basis, and also the usually large, often round table around which the group meets. A Stammtisch is not a structured meeting, but rather a friendly get-together.
Traditionally, the meeting table is marked with a somewhat elaborate sign reserving it for regulars. Historically, such a meeting might involve socialising, card playing (such as skat), and often political or philosophical discussions. The words " Stammtischpolitik" (Stammtisch politics) and " Stammtischniveau" (Stammtisch level), describe the simplified nature of Stammtisch discussions, and have an established metaphorical usage in describing simplified political and social discussions beyond the Stammtisch itself.