la fiebre NOUN temperature; fever
You’re most likely to come across fiebre referring to someone’s temperature, for which it’s the usual word:
No tenía fiebre. He didn’t have a temperature.
La enfermedad lo mantiene en cama con 40 grados de fiebre. The illness is keeping him in bed with a temperature of 40 degrees.
Le ha bajado la fiebre. Her temperature has come down.
It also has the same meaning – fever – as the English word it resembles.
la fiebre amarilla yellow fever
In this meaning it can also be used metaphorically:
la fiebre del oro gold fever
la fiebre electoral election fever