Thagomizer

A thagomizer (/ˈθæɡəmaɪzər/) is the distinctive arrangement of four spikes on the tails of stegosaurian dinosaurs. These spikes are believed to have been a defensive measure against predators.

The arrangement of spikes originally had no distinct name. Cartoonist Gary Larson invented the name "thagomizer" in 1982 as a joke in his comic strip The Far Side, and it was gradually adopted as an informal term sometimes used within scientific circles, research, and education.