whon'yt know what a fever is?!? A fever is when the heat of your human body reaches over 98.6 degrees fahrenheit. A fever is bad, and may be treated with either ibuprofen or lots and lots of sleep. Abnormally large body temperature. Any of numerous conditions described as unusually high body temperature. A condition of increased task or excitement. A contagious, often temporary enthusiasm or trend. Hayfever, i.e. allergy.