Knockback

Knockback is a game mechanic that pushes a player or mob away when they are hit.

Increasing knockback

 * enchantment
 * enchantment
 * potion
 * - ability applies large knockback to all mobs in a radius.

Knockback Resistance

 * - provides immunity to knockback from mobs.
 * (Pet Item) - provides immunity to knockback.
 * - ability provides immunity to knockback.
 * Rotten Armor - Gain additional  knockback resistance to arrows.
 * Tank - Class Passive: Defensive Stance Grants immunity to knockback from mobs.

True Knockback
True Knockback is a type of knockback that ignores all anti-knockback items. It's similar to, but applies to knockback.

Sources:
 * Non-Dungeon bosses:
 * Ender Dragon's Fireball attacks
 * Revenant Horror and Sven Packmaster's anti-cheese attacks
 * Dungeon bosses:
 * Bonzo's Balloon barrage, as well as the attack in his Blood miniboss version
 * Necron's wither skull attack ignores all knockback resistance
 * The Undead Warrior summoned by Scarf when it hits a Player with Warrior's Charge
 * Dungeon mobs:
 * Some of Thorn's minions deal true knockback
 * Lost Adventurer's "Dragon's Breath" Ability
 * Withermancer's homing skull deals heavy true knockback upon implosion
 * Defend Jerry's Workshop Magma Cubes' attacks

True Knockback Resistance
These mounts give you True Knockback Resistance while riding, but removes the Immunity Ticks (10 ticks, 0.5s), that can cause you to die easily.
 * - knockback immunity while riding.
 * - knockback immunity while riding.
 * - knockback immunity while riding.

Tips

 * The knockback enchantment is often considered as a negative thing because that pushing enemies away causes it to take longer to kill, making chain hits harder to get. In most cases, the default knockback applied by weapons is considered sufficient.