Mill
Milling is an informal game term. Milling means to discard cards from the top of a deck. "Mill" on its own implies discarding cards from your opponent's decks, but some cards "self-mill," discarding cards from your own deck for some benefit. 
Dwarven culture specializes in both, with cards like Dwarven Axe (1C9)
and Realm of Dwarrowdelf (2R12)
. Mill strategies often combine with discard strategies, because forcing your opponent to discard cards means they draw more cards when they reconcile, burning through their deck more quickly.
Self-mill decks often use cards like Úlairë Nertëa, Messenger of Dol Guldur (1U234)
or Preparations (7R12)
to fetch lost cards from your Discard Pile. Self-mill decks also often use cards like Ring of Artifice (17R4)
or Úlairë Lemenya, Dark Enemy (19P37)
, which are empowered by spotting cards in your discard pile.
The term comes from Magic: the Gathering, so named after the card Millstone.
