White supremacism is a historical political movement which 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.
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.
"White supremacy" was a term used by some organizations in the United States such as some Ku Klux Klan as late as the 1960s. Today such groups and similar organizations usually refer to themselves as White Nationalists.
More generally the term 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.