Beltaine or Beltane (/ˈbɛlteɪn/) is the Gaelic May Day festival. Most commonly it is held on the 1st May, or about halfway between the spring equinox and the summer solstice. Historically, it was widely observed throughout Ireland, Scotland and the Isle of Man. In Irish it is Bealtaine ([ˈbʲal̪ˠt̪ˠənʲə]), in Scottish Gaelic Bealltainn ([ˈpjaul̪ˠt̪ˠɪɲ]) and in Manx Gaelic Boaltinn or Boaldyn. It is one of the four Gaelic seasonal festivals—along with Samhain, Imbolc and Lughnasadh—and is similar to the Welsh Calan Mai.
Beltane is mentioned in some of the earliest Irish literature and it is associated with important events in Irish mythology. It marked the beginning of summer and was when cattle were driven out to the summer pastures. Rituals were performed to protect the cattle, crops and people, and to encourage growth. Special bonfires were kindled, and their flames, smoke and ashes were deemed to have protective powers. The people and their cattle would walk around the bonfire, or between two bonfires, and sometimes leap over flames or embers. All household fires would be doused and then re-lit from the Beltane bonfire. Doors, windows, byres and the cattle themselves would be decorated with yellow May flowers, perhaps because they evoked fire. In parts of Ireland, people would make a May Bush; a thorn bush decorated with flowers, ribbons and bright shells. Holy wells were also visited, while Beltane dew was thought to bring beauty and maintain youthfulness. Many of these customs were part of May Day or Midsummer festivals in other parts of Great Britain and Europe.
Beltane celebrations had largely died-out by the mid-20th century, although some of its customs continued and in some places it has been revived as a cultural event. Since the latter 20th century, Celtic neopagans and Wiccans have observed Beltane, or something based on it, as a religious holiday. Neopagans in the Southern Hemisphere often celebrate Beltane at the other end of the year (~1 November).
Source: Wikipedia under 'Beltane'.