What do poppies represent?

In 1918, just before the armistice of World War I took effect, a woman named Moina Michael read a poem written in 1915 by Canadian Lieutenant Colonel John McCrae titled "In Flanders Fields." Poppies are mentioned in this poem and so she decided to use and wear red poppies to honor those who had perished in war. Ms. Michael also wrote a poem in response. She chose red to represent the blood that was spilled. The custom soon spread to other countries. However, in the US this tradition applies mostly to Memorial Day and not Veterans Day.