What is "thagomizer"

n. An arrangement of spikes found on the tails of various stegosaurs.

A thagomizer is the distinctive arrangement of four to ten spikes on the tails of stegosaurid dinosaurs. These spikes are believed to have been a defensive measure against predators.

The arrangement of spikes originally had no distinct name; the term Thagomizer was coined in 1982 by cartoonist Gary Larson in his comic The Far Side, and thereafter became gradually adopted as an informal term within scientific circles, research, and education.