Note: this page covers the Standalone version of DayZ; for information on the Mod, see Mod:Nails.
Nails are part of the crafting system recently introduced in DayZ 1.8. They are currently used by two recipes (baseball bat variants), but will be expanded in future versions.
They are a fairly common item, found in the Supermarkets, residential and farm buildings. They take up 1 slot and do not stack.