Weapon flags and special item properties

At identifying items you can see their special properties and flags. External properties (auras, extra-flags) exist for all items; weapon flags only exist on weapons. Some properties are obvious right away, and some are worth explaining in more detail.

ITEM PROPERTIES

Glowing: the item can be seen in the dark without a lantern
Humming: a vibrating item can be worn or used even while blinded
Dark: paladins cannot cast bless weapon on it
Fiendish: a red aura, visible with detect evil. Like dark, it blocks bless weapon. The property CAN be removed with an ordinary blessing prayer, if the prayer overpowers the evil and the item is not protected from enchantment. It adds no damage against good opponents. A curse puts it on together with the "cannot remove" property.
Magical: a member of the Battleragers under spellbane cannot wear this item -- the magic strikes back at them
Blue aura: a blessed item
Holy: a blessed item: to curse it, the blessing has to be broken first. While the blessing prayer itself lasts, it also slightly improves spell defense. It adds no damage against evil -- that is the "holy" weapon flag
Hovers: floats in the air and on water -- it will not fall out of an air room, and a weapon with this flag will not sink if you are disarmed in an underwater fight.
Rots with the corpse: crumbles to dust 5-10 ticks after you die -- try not to die!
Indestructible: cannot be destroyed by any means, in combat or by skills
Visible to ghosts: only ghosts can see this item, wherever it is: on its bearer, on the floor or in a chest. When whoever carries it dies, the property goes away, and the item in the corpse is visible to everyone. Some powerful and rare artifacts hide this way -- which is why they are so hard to find.
Cannot remove: a worn item cannot be taken off, and a weapon cannot be knocked out of your hands. A remove curse prayer can lift it.
Cannot drop: the item cannot be dropped, given away, put in a container or sold. Also lifted by remove curse.
Uncurable curse: remove curse has no effect on this item.
Fireproof: the item will not catch fire, and acid, lightning, sand and sound will not damage it. It can still melt or heat up.
Vanishes on the ground: the item disappears when dropped on the ground.
Cannot enchant: the bless prayer, a curse and enchanting have no effect on this item.
Invisible: only those who detect invisibility can see the item.
Not for good/neutral/evil: creatures of that alignment cannot wear this item, and sometimes cannot even pick it up.
Personal: see personal items. Many other auras are only shown in screen-reader mode.

WEAPON FLAGS

Fiery: burns the opponent with fire, heats up their gear and can blind them with the heat
Frosty: chills the opponent and their gear
Vampiric: every hit drains a bit of life and heals the wielder
Honed: while not worn dull (identify shows it), now and then lands a much heavier blow
Shocking: strikes the opponent with a lightning discharge that hits their gear too. The shock can briefly paralyse
Poisoned: can poison the opponent in combat
Ghostly: passes straight through parry and cross block, unless the defender holds a holy weapon. The spell blade of darkness gives an anti-paladin's shadowblade this property
Holy: in the hands of a good character, sometimes hits evil opponents much harder
Two-handed: takes both hands, so most races cannot carry a shield with it. Large races and bigger (trolls, centaurs, uruk-hai, giants) still can, and only huge ones (giants) can wield a second weapon next to it
Deadly: the weapon occasionally comes alive in battle, cutting off opponents' heads.