Randart is short for random artifact. The Darklands Dungeon produces most of the best weapons in the game through a random process wherein various weapon types can be found with a random number and type of special enchantments. These weapons are rare, but do not dest.

They are usually found unidentified. The article "an" will often give them away. ("an dagger" could be "an acidic keen unholy dagger") Take them to an oracle to discover their enchantments. (glowing) enchants are always visible, but still need to be identified to see what else they are.

Other dungeon gear is detailed on the excellent EotL wiki.

All weapons of this type require 200/100 stats. (200+ on your highest stat, all others 100+) If you don't have high enough stats you will get one of these messages:

You haven't nearly the power to use this. (Your highest stat is too low)
Your weakness prevents you from wielding this. (Your lowest stat is too low)

Different weapons are more than just flavor text. They can have different damage and speed modifiers, and damage types. Some are better for specific use cases.

Randart weapons can be traded with the dwarven merchant. He will take 3 weapons and drop one new one. He wanders the dungeon, but can also be summoned anywhere with the "dwarven raincheck" scroll. To trade, drop the weapons on the ground and then type "trade weapons".

The merchant will ONLY trade randarts. Not all weapons found in the dungeon qualify. All weapons can be found without enchantments, plus there are some magic weapons which are
NOT Randarts: