Some of the terms commonly used on in the Dominion community include:
Base: The original Dominion, with no expansions. E.g., “In base, Chapel is the best early-game trasher.”
Big Money: Strictly speaking, a strategy where no Actions are bought at all, only Treasure and Victory. In practice, often used to refer to a strategy emphasizing Treasure and Victory cards that is merely supplemented with one or two Actions. Compare Engine.
Board (or Set, Table, or Tableau): The set of cards that make up the game of interest.
Cantrip: Any card that gives at least +1 Card, +1 Action; it costs no action to spend it and it replaces itself in the hand. Can technically refer to Villages, but in practice usually refers to cards like Spy.
Chain: A deck in which the same card(s) are played either multiple times per turn (or simply every turn for some powerful cards). E.g., “Lab chain”.
City Trap: Purchasing multiple Cities in a game in which no piles (other than Province or Colony) are likely to be emptied; the Cities are very expensive Villages in this case.
Clog (or Bloat, Gum Up…): Add cards to a deck (preferably an opponent’s) that interfere with the engine being used. Often happens voluntarily in the endgame.
Colony Game: Any game in which Colony and Platinum (from Prosperity) are available for purchase.
Counter: A card that acts to neutralize another card (usually an attack), whether directly (e.g., Moat) or indirectly (e.g., Library vs. Militia/Goons).
Cycling: To move quickly through your deck. Chancellor provides an extreme example of cycling, but cards like Warehouse and Laboratory also cycle your deck effectively.
DoubleJack: A strategy involving buying only two copies of Jack of All Trades, and otherwise exclusively Treasure and Victory cards.
Draw Dead: Generally refers to drawing an Action card when you have no more Actions to play. In context, may refer to drawing an Action card that cannot be effectively used (e.g., Baron without Estate, Moneylender without Copper).
Duchy Dancing: Towards the end of a game, when both players are buying Duchies and neither side is willing or able to take the final Province(s)
Early Game: Most purchases are low-cost cards; players are defining their overall strategy.
Endgame (or Late Game): Players are purchasing almost exclusively victory cards. Often accompanied by jockeying with lower-value victory cards, e.g., PPR.
End on piles: Force the game to end by emptying three or more piles (four or more with 5+ players).
Engine: Loosely defined, the Action cards that “drive” one’s deck. An “engine-based” strategy refers to a strategy emphasizing Actions. Compare Big Money.
Envoy/Big Money: see Smithy/Big Money
Greening / “Go Green”: Begin purchasing victory cards.
Isotropic (or Iso): http://dominion.isotropic.org — an exceedingly popular online implementation of Dominion, often linked to from these forums.
Midgame: Most purchases are actions or treasures of value $5 or higher, but rarely with hands above $6 (Province game) or $9 (Colony game); players are refining their strategies and attempting to tune their engines.
Mirror Match: When both players pursue identical or near-identical strategies
Non-Terminal (or Non-Terminal Action, sometimes NT): Any action card that gives at least one additional Action.
Opening: Purchases made on the first two turns. Usually clarified by a 4/3 or 5/2 opening.
Piles: see “end on piles”
Province Game (rarely, Non-Colony Game): A standard game in which Colony and Platinum are not available.
Pseudo-Trash: Remove cards from your deck without trashing them, e.g., Island.
Sift: Filter through your cards by removing unwanted cards. Similar to cycling, but with more finesses. See, e.g., Warehouse.
Smithy / Big Money: A strategy involving one purchase of a Smithy and otherwise exclusively Treasure and Victory. Reaches 4 Provinces in approximately 14 turns.
Split: Treasure values of the first two hands (5/2 or 4/3). Tournament and league play often gives players the same split.
Terminal (or Terminal Action): Any action card that does not provide another Action when played.
Terminal clash: Drawing multiple terminal cards together, such that you can only play one of them
Terminal Silver: Any terminal action that gives $2.
Top-Deck: Place a card on top of your deck that would normally go elsewhere (e.g. Alchemist, Royal Seal).
Trasher (or Deck-thinner): Any card that allows one to remove cards from one’s deck.
Trash-for-Benefit: Any card that gives a benefit at the cost of trashing a card. Apprentice draws additional cards, Salvager gives cash, etc.
Village: Besides the card of the same name, can refer to any card which gives +2 Actions; most (but not all) such cards have “Village” in their names.
Village Idiot: Village seems like a great card to an inexperienced player, and it is good–but taking Villages without any terminals makes the Villages worthless. Hence, Village Idiot. More loosely, refers to any poor strategy that buys too many Actions.
Virtual +Buy: Cards like Ironworks and Workshop, which allow you to gain an additional card on your turn along with your ordinary Buy
C, S, G, E, D, P: Sometimes used in game analyses for the basic treasure cards and basic victory cards.
BM: Big Money (rarely, Black Market, in context)
BMU: A particular algorithm for playing Big Money that intelligently purchases Duchies
FV: Fishing Village (rarely, Farming Village, in context)
GM: Grand Market
Hag: Sea Hag
HoP: Horn of Plenty
HP: Hunting Party
HT: Horse Traders
IGG: Ill-Gotten Gains
JoAT: Jack of All Trades
KC: King’s Court
MV: Mining Village
NV: Native Village
PPR: Penultimate Province Rule
TFB / T4B: Trash-for-benefit
TM: Treasure Map
TR: Throne Room (rarely, Trade Route, in context)
UAS: Unstoppable Alchemist Stack
UCS: Unstoppable City Stack