In Dead Island, all melee based weapons have Durability (the white bar around the weapon and the base stat shown). When durability is depleted, the weapon will be ineffective, meaning the player can't upgrade it and the damage dealt is less than with their fists; they'll also lose any bonus from mods.
A weapon's appearance slightly changes as its durability decreases. Bladed weapons start bending and getting heavy nicks and dents, while blunt weapons also start bending and getting large cracks in the wood (if hammers, sledgehammers, bats) and such.
Durability being depleted is caused by using the melee weapon towards an enemy. This means that the player can still hit objects and walls, and not lose durability, but they'll still lose it if they hit not-yet-decaying corpses. It is depleted much faster when not upgraded. Throwing a weapon does not deplete its durability. Mods can decrease the maximum durability of a weapon by up to 2 points.
Sharp weapons tend to have lower durability than blunt weapons, sometimes even half the durability, but also tend to have much less force, and do much more damage, whilst blunt weapons usually have more durability, do less damage, and have very much more force. Bladed weapons can also take more powerful mods than blunt weapons.