Fever blisters are small, painful, and contagious sores that can appear on the lips or around the mouth. They are often caused by viral infections like herpes simplex virus (HSV). There are several synonyms for fever blister, including cold sore, oral herpes, herpes labialis, and herpes simplex virus type 1 (HSV-1) infection. The terms "cold sore" and "fever blister" are the most commonly used interchangeable terms for the same condition. Herpes labialis refers to the location where the virus is more common to occur- around the lips, while oral herpes is the broader term used for HSV-1 virus infections anywhere in the mouth.