"Mill" is a colloquial term that originates from the card Millstone, used here to mean "putting the top cards of a player's library into his or her graveyard." For example, you could say, "In the finals of the Pro Tour Qualifier, Herbert cast Tome Scour to mill away my final five cards, dashing my chances of playing on the Pro Tour." There are many players who will play with Tome Scour in their decks
This seems like a better note to wrap up on: For a long time, this was the cause of a lot of rules headaches
In addition to buffing up your arboreal attack force, Verdeloth also offers you the option of a side-line in Saprolings, which can provide a welcome bit of board presence in what is usually a go-tall strategy
Meanwhile, Treasure Mage provides finishing power with Mindslaver, Wurmcoil Engine, or basically any big, powerful artifact you can imagine
Its powerful in EDH where you can swipe game-enders like Ruinous Ultimatum and Breach the Multiverse