Lexicon

A forced variation, normally involving a sacrifice, intended to be to the benefit of the player making it. It is made up of basic tactical ideas combined together as needed.
A combination either works or it doesn't.

Positional advantage which balances the loss of material. This advantage can be: better piece mobility, more space, command of open lines, and so on. It's not always easy to prove if the compensation is sufficient and it is mainly a matter of experience to know if the compensation is worth the material invested.

The stabilisation of a loose position. For example, a player gains material but the effort leaves his pieces scattered incoherently. He consolidates by bringing his pieces back into play, co-operating again and thus exploiting his material advantage.

A pinning piece that becomes pinned itself.

See Opening...

A tactical maneuver consisting of an enemy piece being deflected away from controlling a vital square or line.

A pawn or piece, that is lost anyway, is used to inflict as much damage as possible before it is captured.

A tactical move consisting of the removal of a key piece holding the opponent's position together or defending its own King, even if it has to involve material sacrifices.

Check from a piece that comes to existence by moving away another piece, therewith opening a line or diagonal from where the check originates.
A well-known example is:
1.e4 e5 2.Nf3 Nf6 3.Nxe5 Nxe4? (a blunder; best is 3...d6) 4.Qe2 Nf6 5.Nc6+.
The check is given by the Queen but was caused by moving away the Knight from the e-file. Black loses his Queen.

A check delivered by two pieces at the same time. A double check necessarily involves a discovered check.
It is a powerful move since the opponent has no other option but moving his King away.

A position where both Bishops are fianchettoed: on b2 and g2 for White, or on b7 and g7 for Black.

Two pawns of the same colour on the same file.

Doubled pawns are generally weaker than two 'normal' pawns. It has been said that they have the defensive power of two pawns but the attacking power of only one.

One of the possible outcomes of a chess game as a tie, case when both players split the point equally. This can happen if both sides agree to it at any moment in the game, or neither side can win in any of the following situations:
- stalemate;
- threefold repetition;
- 50 moves rule;
- not sufficient material to checkmate.
If any of the above cases occurs, the game is called a draw immediately.

It is the acronym for Encyclopaedia of Chess Openings which is a book collection (now also available as a computer database) describing chess openings. The moves were taken from hundreds of thousands of games between masters, from published analysis in the "Chess Informant" since 1966, and then compiled by notable chess players. Both the ECO and the "Chess Informant" are published by the Serbian company Sahovski informator.
All known openings are divided into 5 main codes A-E and several numeric subdivisions.

Source: "Wikipedia, The free Encyclopedia"

A special method of capturing available only to a pawn on its 5th rank: if an enemy pawn on an adjoining file were to be advanced two squares in one move it could be captured as if it had been moved one square only. An 'en passant' capture may be made only on the move immediately following such an advance.
'En passant' is French for 'while passing by'.

The stage of the game when there are few pieces left on the board. The endgame follows the middlegame.

Source: "Wikipedia, The free Encyclopedia"

It divides the board in 2 sides: the Queen side (4 files) and the King side (4 files), to go together with the regular 8 ranks. From here on things get a bit more complicated:
a) 2 sides - each file is marked by a combination of letters: one after the side is located on and the second after the piece residing there in the original position. Example: QN = Queen's Knight means the second file counting from the left hand side of the board.
b) 8 ranks - each player counts the 1-8 ranks beginning with the nearest and ending with the farthest. This creates confusion since what is considered the 8th rank from White's perspective, it actually is considered 1st rank from Black's perspective and so on.
Example: 1.e4 e5 is equivalent to 1.P-K4 P-K4
Several books published in English were originally written in English descriptive notation during the first half of the 20th century. Fortunately the algebraic notation prevailed and quite a few of those books have been reprinted since the 90s.

It is a type of checkmate where two parallel retreat squares for a checked King are occupied by his own pieces, preventing his escape. They are compared with the ornamental shoulder pieces worn on military uniforms called "epaulletes" (French), giving the checkmate its name.

General: trading one piece for another of the same value.
In the special case of trading a minor piece (Bishop or Knight) for a Rook, the player capturing the Rook is said to have "won the exchange".

Italian word (fianchetto=little flank) meaning the development of a Bishop on the flank: g2 or b2 for White, g7 or b7 for Black.

One rule to stop a game from going on forever. It states the game can be declared a draw if no pawn move or capture has been made for 50 consecutive moves.
If a pawn move or capture occurs at anytime during those 50 consecutive moves, the move count restarts from zero.

A column of the chessboard. A specific file can be named either using its position in algebraic notation, and/ or by using its position in English descriptive notation. Example: the f-file or the king bishop file comprises the squares f1-f8 or KB1-KB8.

Source: "Wikipedia, The free Encyclopedia"

A simple yet most effective tactical device consisting of one piece directly attacking two or more enemy pieces simultaneously. The Knight is one of the deadliest pieces to deliver a fork!

An opening in which one player offers to give up material, usually a pawn sometimes a piece or more, in the expectation of gaining positional compensation. The word gambit is derived from the Italian word 'gambetta', a wrestling term for tripping up the heels, and was first used in its chess sense by Ruy Lopez in 1561.

The record of a game in some form of notation