Breakable

Breakable equipment (both armour and weapons) will slowly get more worn out and battered as it is used in combat. The more battered a piece of equipment, the greater chance that it will break. There are various means of repairing worn equipment, and most can be repaired when broken (although the cost is sometimes too high to make it worthwhile)

Examining a piece of equipment will show its current state of repair, or it will say "It looks unbreakable." if it is unbreakable. You can also see the state of all of your equipment by checking eq, where the colour indicates the state of repair of each worn/wielded piece.