Bon is the buddhism-based Japanese custom, but a traditional event rather than religious I think. During the 3 summer days (the particular dates vary depend on the area) the spirits of ancestors visit the household so the families clean the graves or put flowers or food in front of butsudan - wooden cabinet looks like a small shrine in Japanese homes in which we keep Ihai (buddhist memorial tablet for the deceased family members) - or invite the priest to recite a sutra, etc.
This is the first Bon for our new house, and tomorrow the buddhist priest of our family temple (in my grandfather's home town) will visit here. Mother put the offering (flowers and food) in & around the butsudan. I thought this photo might interest my foreign friends even without the knowledge about Bon.