Each character has one "radical" out of a set of 214, which was assigned by the Kangxi emperor about three centuries ago as a way to index and sort characters.

Each character has one "radical" out of a set of 214, which was assigned by the Kangxi emperor about three centuries ago as a way to index and sort characters. Sometimes it's the whole character itself, sometimes it's a clear part of a character, sometimes it has to be pointed out. Some or all or none of the other components of a character may also be radicals or not. Westerns use "radical" to mean any component but I don't know whether that's common among Chinese or Japanese people as well.