It's May Day, which means different things to different people. Originally it was a pagan celebration centered around the Celtic god of light. Then it became simply a celebration of spring, with dancing around the Maypole as one feature of the festivities. International workers around the world chose May 1st to march in support of their members and in protest against unfair wages and labor laws.
I remember hanging May baskets on doorknobs of friends' houses as a child in Iowa. The homemade baskets would be filled with early spring flowers, and the goal was to knock and then run and hide so the recipient wouldn't know who had left the flowery gift.