The second Sunday in May is Mother's Day. On this day, people give carnations as a way of saying "thank you" to their mothers, who raised them with loving care. Mother's Day originated in the United States, but it's spread to countries around the world, so you're probably familiar with it.
In Japan it was first observed by Christians starting around 1913, and by the 1930s large gatherings were being held to celebrate Mother's Day. The practice was halted during World War II, when Western customs were prohibited, but it was revived after the war, partly as a means of consoling the women and children who lost their husbands and fathers in the war. By 1949 the practice had spread to all parts of the country.
Mother's Day is celebrated throughout Japan today. Kids show their appreciation by buying gifts and helping out with the chores. Special events are usually held at department stores and shopping districts, and at some elementary schools, kids make presents for their mothers or draw portraits of their moms in class.