A fundamentalist is someone who believes in following what they see as the most basic, original teachings of a religion exactly as they understand them, without changing or reinterpreting those teachings for modern times. The word comes from fundamental, meaning the essential foundation or core of something.

Fundamentalists believe that certain religious texts should be read and followed literally, word for word. Sometimes, this can lead them to support very strict rules or behaviors.

Fundamentalism refers to this way of believing. While fundamentalists see themselves as protecting important truths from being watered down, critics worry that fundamentalism can make people rigid or intolerant of different viewpoints. A key characteristic is insisting that there is only one correct way to understand and practice a faith, usually based on a literal reading of ancient texts.