White supremacism was a historical political movement that believed that Whites are superior to some non-White populations and therefore should control or rule these groups (possibly for the benefit of all groups). Nowadays, there are virtually no White supremacist organizations in the world.
In contemporary political discourse, the term is primarily used as a straw man label on individuals and groups simply supporting the interests of Whites, despite a similar label not being applied to individuals and groups supporting the interests of non-Whites, thus also meaning a double standard regarding applying such labels.
Claims of "White supremacism" are routinely applied by groups such as the SPLC and the ADL to disliked individuals and groups, without citing evidence showing actual support for "White supremacist" views. Such unsupported claims are then mass repeated by the politically correct mass media and politically correct websites such as Wikipedia.
More generally, the term "White supremacism" has been applied to historical movements supporting White colonialism. Such colonialism was not necessarily motivated by self-interest, but could be motivated by a desire to improve the situation for non-Whites. See the Colonialism article.
Strangely, pro-White organizations are often implied to want to Holocaust others due to being often falsely implied to be (concealed) National Socialist organizations, despite that virtually all National Socialist organizations have been Holocaust revisionist.