Political radicalism (from Latin "radix" meaning root) is a term that has had several different meanings, but generally involving ideological desires to make very large political changes.
The term has often been applied to left-wing movements, but also more recently to some right-wing movements, although left-wing sources may often prefer more perceived derogatory terms, such as "reactionary", "extreme right", "far right", and "populist right".
Leftist Wikipedia claims that in the United States, "radical right" " is "a strictly conservative and anti-socialist tendency in US politics", while in Europe, "radical right" is "a nationalist and populist tendency in European politics".
Radicalisation or radicalization refers to becoming more politically radical, such as on the left–right political spectrum.
However, the word may also refer to becoming more radical more generally, including regarding religion, such as in Islamization.
Such radicalization can be both nonviolent and violent. However, many sources use the word in association with terrorism. There may be attempted guilt by association, attempting to associate explicitly non-violent views with terrorism in order to try discredit the views.