Short Answer:
Sores that form around the mouth and lips.
Long Answer:
Cold sores are groups of small blisters that form on the lips and around the mouth. The skin around the blisters can be red, swollen, and sore. The blisters may break open, leak a clear fluid, and then scab over after a few days. They usually heal after several days to 2 weeks, and are also commonly referred to as fever blisters.