A hallmark holiday is a special day or event that people celebrate, like Valentine's Day, Mother's Day, or Father's Day. These events are called "hallmark holidays" because they were invented by companies that make greeting cards and other gifts. They are not official holidays like Christmas or Thanksgiving, but they are still important to many people. Some people believe that these holidays are too commercial and that they focus too much on buying presents rather than spending time with loved ones. However, others enjoy these holidays because they provide an excuse to do something special for someone they care about. So, in short, a hallmark holiday is a special day that some people celebrate because it was created by companies to sell greeting cards and gifts.