It was originally known as St. Valentine's day and shortened to Valentine's Day over time, but the sentiment remains the same. It's a day of celebrating love and affection between one another. The day is named after an early Christian martyr named Valentine and was first associated with romantic love during the High Middle Ages, when courtly love was popular.
The date derives its name from several Christian martyrs from the early hundreds, AD. There were several different martyrs that the name was taken from and at the time they had no romantic leanings. One specific Valentine is said to have been martyred in Africa on February 14th and that's where the date came from. The romantic aspect of the holiday comes from Geoffrey Chaucer who wrote, "For this was Saint Valentine's Day, when every bird cometh there to choose his mate." These words were included in a poem that honored the engagement of teenagers King Richard II of England to Anne of Bohemia.
Critics mistakenly assumed he was referring to St. Valentine's Day of February 14th, although that is not a time when birds would be mating. In his text, Chaucer makes it seem like it it's an old tradition, although it doesn't appear to have existed prior to his writing it.
It seems only just that the city of love, Paris, adopted a High Court of Love on February 14, 1400. This was run by women on the basis of their poetry reading ability or the earliest written valentines. The holiday flourished and England embraced the celebration with the forming of factories that assembled paper valentines.
While the earlier forms of valentines were hand written poems, they eventually gave way to the manufactured forms. From paper valentines to gifts such as chocolates, flowers, and other romantic gifts, the traditions surrounding Valentine's Day have blossomed like the roses so popular on that day. It is estimated that 190 million valentines are sent each year in America alone, mostly among children. Although it's jokingly called, "Singles Awareness Day," it's still a time for all people to remember to express to their loved ones their un-dying love.