2-Bet
The first raise. Preflop, this is the same as an "open". Postflop, it is a raise of a bet.

3-Bet
A raise of a raise (a re-raise).

4-Bet
A raise of a 3-Bet.

5-Bet+
A raise of a 4-Bet, and any raise after that.

Backdoor Flush
A flush that is made after having only three to a flush on the flop, and thus needing both the turn and river cards to complete the flush.

Backdoor Straight
A straight that is made after having only three to a straight on the flop, and thus needing both the turn and river cards to complete the straight.

Blocker
Any card that, because it is in your hand, reduces the number of hands that your opponent(s) can have or make containing that card/rank.
example: If you have a Jack in your hand, on a 8-9-Q-x-x board, it reduces the chance that your opponent has a straight.

Big Bet (BB)
In a fixed-limit game, it is the larger of the two bet sizes. For example, in a $4/$8 Limit Hold'em game, the Big Bet amount is $8.

Big Blind (bb)
The larger of the two forced bets in any game with blinds. For example, in a $1/$2 No Limit Hold'em game, the Big Blind amount is $2. Sometimes the amount of chips a player has in front of him is measured in big blinds.

Check Raise
Raising an opponent's bet after having initially checked.

Cold Call
Calling a raise when you did not make or call the previous bet. For example, you may cold call a preflop 3-Bet, having not made or called the original 2-Bet.

Cold Raise
Making a raise when you did not make or call either of the TWO previous bets. For example, when facing a 3-Bet, when you have not called or raised the original 2-Bet, you have the opportunity to make a ‘cold 4-Bet’.

Continuation Bet (C-Bet)
A bet on the flop made by the preflop raiser. Also applies to a bet on the Turn by the preflop raiser (assuming he/she bet the Flop) and a bet on the River by the preflop raiser (assuming he/she bet both the Flop and the Turn).

Cutoff (CO)
The position directly to the right of the Button.

Delayed Continuation Bet
Also known as a “Delayed C-Bet”. A bet on the turn by the preflop raiser, after the flop was checked through (no betting).
example: Player A raises preflop and Player B calls from the big blind. On the flop, both players check. On the turn, Player B checks and Player A bets. Player A’s bet is a “Delayed Continuation Bet”.

Donk Bet
An out-of-position bet made on the flop, turn, or river before the aggressor on the previous street has had a chance to act.
example: Player A raises preflop and Player B calls from the big blind. On the flop, Player B is first to act and bets out. Player B’s bet is a “Donk Bet”.

Double Gutshot
A hand that contains two different gutshot straight draws simultaneously, thus giving it the same number of outs (8) as an open-ended straight draw.
example: T9 on a board of 6-8-Q

Effective Stack
At any point in the hand, the Effective Stack is equal to the smallest of the active stacks remaining in the hand.
example: Player A, Player B, and Player C all see the flop. Player A has $150, Player B has $250, and Player C has $100. On the flop, the Effective Stack is $100.
example: Player A and Player B are heads-up to the Turn. Player A has $125 and Player B has $200. On the Turn, the Effective Stack is $125.

Early Position (EP)
Being one of the first players to act, such as the under-the-gun position. The exact number of positions deemed to be “early position” will vary, depending on the table size.

Equity
At any given point in the hand, your equity is the percentage of the pot that you will expect to win over an infinite number of samples. In other words, it is the percentage chance that you have of winning the pot. In monetary terms, your equity is equal to your percentage of winning the hand multiplied by the total pot.

Expected Value (EV)
The average amount won or lost for a given bet/hand/situation/etc., considering all of the possible outcomes and their probabilities.

Float Bet
An in-position bet made after having called a bet (or preflop raise) of the preflop raiser on the previous street.
example: Player A raises preflop and Player B calls in position. On the flop, Player A bets and Player B calls. On the turn, Player A checks, and Player B bets. Player B’s bet is a Float Bet.

Freezout
A tournament that has no re-buys or add-ons.

Game Theory Optimal (GTO)
Game Theory Optimal, or GTO for short, is a highly mathematical approach to poker. It centers around devising a strategy that is balanced and unexploitable.

Gutshot
A straight draw that is completed with only one rank, thus giving it four outs. Also known as an "inside straight draw".
example: T9 on a board of 4-8-Q

Hand History (HH)
A text version (file) produced by an online poker site for every single hand that is played on a given table, or by a given player. It contains the full details of every hand, including stack sizes, positions, bets, board cards, etc.

Hijack (HJ)
The position immediately right of the Cutoff; two seats to the right of the Button.

Inside Wrap Straight Draw
In Omaha, an inside wrap draw is a straight draw with eight or nine outs. It occurs when you have three ranks in your hand that are all outs to your straight (the eight outs scenario occurs when one of these three cards is paired in your hand).
examples:
9 Out Inside Wrap: 789x on T-6-x
8 Out Inside Wrap: 89TT on J-7-x

Kicker
A card that is used to break “ties” when multiple players have the same hand rank.
example: The board is A-9-9-5-4. Player A holds AJ. Player B holds A8. Both players have the same hand rank (two pair, aces and nines), but Player A has a better hand than Player B, since Player A’s Jack kicker is higher than Player B’s 8 kicker.

Last Aggressor
At any point in a hand, last aggressor refers to the player who most recently bet or raised.

Limp
Entering the pot preflop (when there has been no raise) by calling the amount of the big blind, as opposed to raising.

Lojack (LJ)
The position immediately right of the Hijack; three seats to the right of the Button.

Late Position (LP)
Being one of the last players to act, such as the Cutoff and Button positions. The exact number of positions deemed to be “late position” will vary, depending on the table size.

Muck
Another term for ‘fold’.

Nash Equilibrium
Describes a state of poker in which opponents are each playing an optimal strategy against one another, such that they have no incentive to deviate from this optimal strategy. In other words, if one player was to make any adjustments, it would just result in them playing a “less optimal” strategy than their opponent(s).

Nut Flush Blocker
When there are two or more of a given suit on board, the highest rank of that suit that is not on the board.
example:
Ace of Spades on a board of Qs-Js-3s
Queen of Spades on a board of As-Ks-7s

Nut Straight Blocker
Any card that blocks the nut straight.
examples:
All Tens and all Queens on 8-9-J-x-x
All Eights and all Jacks on 7-9-T-x-x

Open-Ended Straight Draw
A straight draw with eight outs, such that one card on either “end” of the draw will complete the straight.
examples:
JT on 9-8-x
75 on 8-6-x
98 on T-7-x

Open Raise
A preflop raise when no one else has entered the pot. Same as Raise First In.

Overbet
Betting more than the size of the current pot.

Overcall
Calling any bet/raise after at least one other player has already done so.

Overcard (to the board)
Any card that is higher in rank than the highest card currently on board.

Overlimp
Entering the pot preflop with a limp when one or more other players have also limped.

PioSolver
A popular software program (“solver”) for analyzing and studying NLH. Solvers are designed to teach you how to play a Game Theory Optimal (GTO) strategy, in which your play will be balanced and unexploitable. Solvers work by having the user input data about the specific situation (hole cards, board cards, stack size, opponents’ ranges, possible bet sizes etc.) and then generating optimal betting frequencies for the different bet sizes and hole cards that were inputted.

Preflop Raise(r) (PFR)
The player who made the last raise preflop. Or in terms of stats/percentages, it is the percentage of times that a given player raises preflop.

Probe Bet
An out-of-position bet after the player who could have made a continuation bet on the previous street failed to do so. A Probe Bet can occur on the Turn or the River.
example: Player A raises preflop and Player B calls from the big blind. Both players check the Flop. Player B bets the Turn. Player B’s bet is a Probe Bet.

Raise First In (RFI)
A preflop raise when no one else has entered the pot. Same as open raise.

Range
All of the possible hands that a player may have in a given situation.

Set
Three of a kind, specifically when you hold a pocket pair and the board contains the third card of that rank.

Showdown
The point at which the best hand is determined and the pot is awarded. A showdown occurs if the river action has been completed and two or more players have a live hand.

Squeeze
A preflop re-raise (3-Bet) after there has been a raise (2-Bet) and at least one call of that initial 2-Bet in front.
example: Player A opens the pot for a raise. Player B calls the raise. Player C "squeezes" by re-raising.

Steal
An open raise by the cutoff, button, or small blind.

Steal Defense
A steal defense situation is when you are in the small blind or big blind, and are facing an open raise by the cutoff, button, or small blind (a steal), and no one else has called or raised.
example: The button open raises. The small blind is then in a steal defense situation. If the small blind then folds, the big blind is also in a steal defense situation. However, if the small blind calls or raises, then the big blind is not in a steal defense situation.

Straight Blocker
Any card that blocks any straight.
examples:
All Eights, Jacks, and Kings on Q-T-9-x-x
All Fours, Sixes, and Nines on 5-7-8-x-x

Under the Gun (UTG)
The player directly to the left of the Big Blind. The UTG player is first to act preflop.

Voluntarily Put Money In Pot (VPIP)
VPIP refers to any time a player enters the pot, excluding times where they check their option from the big blind in an un-raised pot. Therefore, it is any time a player either limps, calls a raise, raises, or completes from the small blind.

Wrap Straight Draw
In Omaha, a wrap draw is a straight draw with anywhere from twelve to twenty outs.
examples:
12 Out Wrap: TT98 on 7-6-x
13 Out Wrap: T98x on 7-6-x
17 Out Wrap: 975x on 8-6-x
20 Out Wrap: KQ98 on J-T-x

Went to Showdown (WTSD)
The percentage of hands that a given player got to showdown with, assuming that he at least saw the flop. So a high WTSD percentage means that the player is more inclined to play hands until showdown, once he sees the flop.

Won at Showdown (WSD)
The percentage of hands that a given player wins, assuming that he went to showdown. For example, a high WSD percentage means that the player wins most of the hands that he goes to showdown with.

Won When Saw Flop (WWSF)
The percentage of hands that a given player wins, assuming that he at least saw the flop in the hand. So a high WWSF percentage means that the player wins more than his fair share of pots once he sees the flop, by either having the best hand at showdown, or forcing the other players to fold before then.