The United Nations and other international bodies such as the International Court of Justice do not legally define "leftism", however they do define things like sexism, racial discrimination (aka racism), ageism, etc and so the same definitions that apply to them can be applied to leftism. By taking the definition for racism and replacing the word racism with leftism the legal definition of leftism becomes: Although that doesn't techinically make any sense, it gets the general idea across well.