Enrage is special kind of buff that affects boss monsters. While monster is enraged weapons' enrage lines and Focused crystals activate. This nearly doubles the party damage output. Also healers should save their buffs with long cooldown for boss enrage.
When enraged boss' status bar glows red and special icon is shown. As of January 2019 update boss status bar also has counter showing remaining time of boss enrage.
Three classes can cast Infuriate to force boss to enrage: Lancer, Brawler, and Warrior in Defensive Stance. Berserker lacks this ability and is considered inferior tank class.
Infuriate should be generally cast at the start of boss fight along with every other buff available. Bosses usually naturally enrage at certain percentages of their health for a fixed period of time. Most bosses naturally enrage at 90% of their health. The faster boss is killed the longer time he spends enraged compared to fight duration.