First day of issue, the first day a postcard, postage stamp or stamped envelope is officially put up for sale
The Church of Jesus Christ of Latter-day Saints | Green Day | One Day International | New Year's Day | Boxing Day | Memorial Day | Seventh-day Adventist Church | Labor Day | Doris Day | Earth Day | May Day | Sandra Day O'Connor | Valentine's Day | Record Store Day | Mother's Day | Ferris Bueller's Day Off | Bastille Day | Six-Day War | April Fools' Day | Australia Day | Father's Day | Brightest Day | Big Day Out | Macy's Thanksgiving Day Parade | Canada Day | Victory in Europe Day | Long Day's Journey into Night | Armistice Day | The Day After Tomorrow | Stockwell Day |
The crew of Apollo 15 took 398 unauthorized commemorative postage stamp covers with them on their trip to the Moon (400 were printed, but two were damaged and destroyed prior to being packaged), with the understanding that, when they returned, 100 of the covers were to be sold to the German stamp dealer who provided them.