Peperos are long thin cookies that are usually dipped in chocolate (or may have chocolate inside). However, they can be coated in other flavors, like strawberry or peanut.
According to Wikipedia: Pepero Day is an observance in South Korea similar to Valentine's Day, but held on November 11. The original purpose of the Pepero Day was to exchange peperos with each other in hopes of becoming taller and thinner. The current purpose is to exchange peperos to show affection for friends and loved-ones.
Naturally, Matt and I will be celebrating. You can find Pepero at any Asian market and you can find the Japanese version, Pocky, at various grocery stores (don't ask me which ones- I just know I've seen them).