Beltaine (there are various spellings of this) is a pagan/wiccan holiday that has descended from the ancient Gaelic holiday Céad Shamhain.
Samhain (Halloween) marked the end of the summer, and Céad Shamhain marked the beginning. The Gaelic people celebrated in early May, enjoying the company of neighbours they might not have seen over the winter. There would be bonfires and all night celebrations before the time when farmers would be busy planting their crops, and herdsmen would need to drive the flocks to pasture.
In modern times, pagans & wiccans celebrate Beltaine on May 1st as the second of the spring sabbats. (The first spring sabbat, Imbolc, in early February, is a time for looking forward with hope to spring).
When Beltaine arrives, one can actually see life renewing itself. Signs of spring are all around. Flowers and trees are budding. The weather is warmer. The days are longer and the air smells of new growth. All of our senses are telling us that winter has ended.
Although traditions and interpretations vary among the various pagan & wiccan faiths, Beltaine is usually seen as a fertility festival. People celebrate to bring fertility to their lands so that their crops will grow well and be abundant, and to their animals so that they will reproduce and thrive. It can also be seen as a time to celebrate to bring fertility to your hopes and dreams.
Some pagans & wiccans see this as a time to fertilize their dreams by taking action to move themselves closer to their goals. Pagans may make lists of things they hope to accomplish in the upcoming summer.
Many countries have a national holiday on May 1st (May Day), but most people do not realise they are in fact recognising a pagan festival by marking this day.