A term used to describe an individual who has a strong sexual fetish-liking towards other individual who possess Scandinavian features, most notably blond hair and blue eyes who also who might exert some degree of Germanophilia/Scandinavian phile.
This term is used in a similar context with an individual who might have a strong fetish for Asians, also known as Yellow Fever.
Viking Fever can also be used loosely to refer to the liking of red-haired individuals (Erik the Red a famous Viking was redheaded) or light haired with light colored eyes individuals. The term can only be applied to individuals who are of Non-European descent (i.e. Africans, Asians, Arabs, Hispanics, etc.) or really dark-skinned/hair Europeans; but no particular race in general, as long as the person being told they have Viking Fever aren't Scandinavian themselves.
Friend 1: Bro I love Taylor Swift, she has such beautiful blond hair and blue eyes
Friend 2: Dude you got Viking Fever!
Friend 1: What's that?!?!?!
Friend 2: Means you have a fetish for blonds!