Nothing lasts forever, just ask my knees. Time was they were spry and full of life, now they grate together like an angry pair of hedgehogs getting in a fight. Equipment is similarly affected. Weapons, armour and tools have a limited amount of durability before they stop working. Think of it like hitpoints for inanimate objects.
You can repair an object at a crafting bench, or you can use certain spells to recover durability. Once an item breaks, it won’t be destroyed, but it won’t be useful until you can repair it. So make sure to keep an eye on your gear’s durability.