Bealtuinn is a Scots Gaelic word derived from older Gaelic and meaning "bright fire". The modern word is Beltane and signifies the start of Summer traditionally dated at the first of May.  Using a solar and lunar based calendar for the seasons the full moon at Beltane could appear any time up to May 7, so that other dates for Beltane may be observed. Fires are lit on Beltane eve and other celebrations are held.

http://www.chalicecentre.net/beltaine.htm
http://www.mojairlandia.pl/tradycje/tr-beltain.php
https://nemedcuculatii.org/lore/wheel-year/witches-sabbats/festfertility/
http://en.wikipedia.org/wiki/Beltane