Enrage is an ability word used for abilities that trigger whenever the creature is dealt damage. It was introduced in the Ixalan expansion and appears primarily on Dinosaurs, encouraging decks to deliberately ping their own creatures and receive something much more useful in return.
Marauding Raptor can damage Dinosaurs as they enter while reducing their casting costs, and Forerunner of the Empire can deal one damage across the battlefield whenever another Dinosaur arrives, enabling enrage. Wayta, Trainer Prodigy pushes the strategy even further by rewarding damage-triggered abilities.