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Pepero is just the snack sold by Lotte confectionary. Actually, it's copied product of Pockey of Japan. But 'Pepero Day' is widely accepted especailly in young people.
Since Pepero has the form of the stick, it looks like number 1. So Lotte started a few years ago calling November 11th as Pepero day, on which people should give pepero to others they love. Yes, it's like Valentine's Day and White Day of Korea. Those 'DAY's were all made by snack company. :P