They are incredibly rare and can fetch a lot of loot in the game's online economy. Mid and high runes should not be parted with easily. A full list of runewords can be found in the next section.
Runewords, as they're called, are some of the most powerful items in the game, right up there with set items and uniques. However, the real magic of runes comes when you combine them in a specific order in a specific item.
Runes are socketable items, just like gems, meaning you can put them into socketed gear to receive their effects. Single runes can drop anywhere in Diablo 2: Resurrected, starting in Normal difficulty through to Hell difficulty.