Mother's Day is a holiday to celebrate the person that brought us into the world, or to the mother figures in our lives. This includes step-mothers, close female role-model friends, aunts, grandmothers and great-grandmothers, and more. Shop here for Mother's Day themed novelty t-shirts. Mother's Day is celebrated all around the world. In many countries, including the United States, Mother's Day takes place on the second Sunday in May.