Cormarë
From Tolkien Gateway
Cormarë or "Ring-day" was a day of celebrations in Fourth Age Gondor. It was held on September 22 (or Yavannië 30) to celebrate the birthday of Frodo Baggins, destroyer of the One Ring.
Uses outside the legendarium
22 September is a popular "ceremonial" date for founding Tolkien societies. Unquendor (the Netherlands), Eredain (Switzerland), Imladris (Denmark) and several others were founded on this day. Another ceremonial day is 3 January, the birthday of J.R.R. Tolkien.
Among fans, 22 September is also commonly observed as the Hobbit Day.