Fascism and nazism seem to be used interchangeably, but are there any differences between these ideologies?
Nazism is a particular brand of fascism. Political scientists have identified fourteen characteristics of fascism. These characteristics will be manifest in various ways from government to government, but they will usually be found in some form or another.
Hitler and the National Socialist German Workers’ Party (Nazi), had their own particular manifestation, most notably the vilification of Jews and the need to exterminate them as a people, and the need to conquer Europe as an empire for Germans. These two features were specific to the Nazis, and are not relevant to other forms of fascism.
The identification of “other” as the source of national grievances, and the identification of a “homeland” which must be militantly protected and expanded for the benefit of a select group, however, are common to all fascist governments.
Here is a list of the characteristics of fascist governments. The specific ways in which these are implemented will vary from one government to another. In short: all Nazis are fascists; not all fascists are Nazis.