It's a common word used for various celebrations, including:
* Religious festivals: Gwyl y Nadolig (Christmas), Gwyl y Pasg (Easter)
* Cultural festivals: Gwyl Dewi Sant (St. David's Day), Gwyl Mabon (Autumn Equinox)
* General celebrations: Gwyl yr Haf (Summer festival), Gwyl y Gaeaf (Winter festival)
You might also see the word "gwyl" used in names of places, such as "Llanfair Gwylfa" or "Llanfair Gwylfaethlwyd."