What does the word "valentines" refer to in the passage?

Although February is a very cold month in many parts of the United States, many nice things happen during February. It is the month when Americans celebrate the birthdays of George Washington, Abraham Lincoln, and Thomas Alva Edison. Washington, for whom the capital was named, was the first president of the United States. Lincoln, who was also a president, is especially remembered for ending slavery in 1862.
     Thomas Edison is the most honored American inventor. He invented the electric light, the phonograph, and movies—three of the world’s most popular items.
     Valentine’s Day also comes in February. It is the day when people give valentine cards or candy to their boyfriends, girlfriends, husbands or wives. Valentines often have the shape of a red heart and a nice way to say, "I love you."
     The entire month of February has been named "Black History Month". Cities, schools and clubs often plan programs to honor the black men and women who have contributed so much to American culture. They have served on the president’s cabinet, on the Supreme Court, and in the United States Congress. Los Angeles, Washington and Cleveland are some of the big cities that have elected black mayors. These black Americans have come far since the days of slavery.