A poster on an Internet forum, (particularly 4chan) who expresses opinions which are either strongly nihilistic, ("life has no meaning," or Tyler Durden's special snowflake speech from the film Fight Club being probably the two main examples) or contain references to Hitler, Nazism, fascism, or other taboo topics which are deliberately intended to shock or offend readers.

The term "edgelord," is a noun, which came from the previous adjective, "edgy," which described the above behaviour.

Someone who jokes about killing themselves but actually wants to but they don't because its a joke and they also like to say they love Hitler and other stuff but they don't actually even though they do.