Unbreaking is an enchantment in Minecraft that gives an item (tools, weapons and armor) a chance to avoid durability reduction when used, thus increasing the durability of the item.
More information on what the unbreaking enchantment is for
You can add the Unbreaking enchantment to any pickaxe, shovel, axe, hoe, fishing pole, carrot on a stick, shear, helmet, breastplate, leggings, boots, shield, elytra, sword, trident, bow, or crossbow using an enchantment table, anvil, or game command. Then use the enchanted item and never see it wear out!
The maximum level for the Unbreaking enchantment is level 3. This means that you can enchant an item up to level Unbreaking III. The higher the level, the stronger the enchantment.
For each higher level the lifetime of the tool is multiplied by the level + 1 (ex: level 4 = x 5).