The international Correspondence Chess Federation, founded in 1951 to replace the International Correspondence Chess Association (ICCA).
Irish Chess Union  publishes ICJ Irish Chess Journal
An abbreviation for the older term International Grandmaster. The modern usage is Grandmaster (GM).
4. Illegal move
A move that is not permitted by the rules of chess. An illegal move discovered during the course of a game is to be corrected.
5. Illegal position
A position in a game that is a consequence of an illegal move or an incorrect starting position.
In chess problems, an illegal position is one that is impossible to reach in a game by any sequence of legal moves.
International Master title.
An increment refers to the amount of time added to each player's time before each move. For instance rapid chess might be played with "25 minutes plus 10 second per move increment", meaning that each player starts with 25 minutes on their clock, and this increments by 10 seconds after (or before) each move, usually using the Fischer Delay method.
8. Indian bishop
A fianchettoed bishop, characteristic of the Indian defences, the King's Indian and the Queen's Indian.
9. Indian defence
A chess opening that begins 1.d4 Nf6. Originally used to describe queen's pawn defences involving the fianchetto of one or both Black bishops, it is now used to describe all Black defences after 1.d4 Nf6 that do not transpose into the Queen's Gambit.
The advantage that a player who is making threats has over the player who must respond to them. The attacking player is said to "have the initiative". s/he can often turn the play as s/he wills. The initiative often results from an advantage in time and/or space. The notion of the initiative was used by Steinitz (e.g. The Sixth American Chess Congress) and by Capablanca in his Chess Fundamentals.
11. Insufficient material
An endgame scenario in which all pawns have been captured, and one side has only its king remaining while the other is down to just a king, a king plus one knight, a king plus one bishop, or indeed a king plus any number of bishops on the same colour as each other (up to nine), as is possible via underpromotion. A king and bishop versus a king and bishop with the bishops on the same color is also a draw. The position is a draw because it is impossible for the dominant side to deliver checkmate regardless of play. Situations where checkmate is possible only if the inferior side blunders are covered by the fifty-move rule.
This happens when the line between an attacked piece and its defender is interrupted by sacrificially interposing a piece.
13. International Arbiter
A tournament official who arbitrates disputes and performs other duties such as keeping the score when players are under time pressure.
14. International Grandmaster (IGM)
The original name of the FIDE title now simply called Grandmaster (GM).
15. International Master (IM)
A chess title that ranks below Grandmaster but above FIDE Master.
16. Internet chess server
This is an external server that provides the facility to play, discuss, and view chess over the internet, also abbreviated ICS.
To move a piece between an attacking piece and its target, blocking the line of attack. Interposing a piece is one of the three possible responses to a check, the others being to move the king or capture the attacking piece.
18. Interzonal Tournament
A tournament organised by the FIDE, the second qualifying cycle of the World Chess Championship. The participants are selected from the top players of the zonal tournaments. The top ranking players qualify for the candidates tournament.
19. Irregular opening
Irregular openings are chess openings with an unusual first move from White. These openings are all categorized under the ECO code A00.
refers to a d-Pawn with no Pawns of the same color on the adjacent c- and e-files, and is a synonym for 'Isolated Queen's Pawn'. The term was coined by Nimzovitch, who considered the isolani as a weapon of attack in the middle game but an endgame weakness; he considered the problem of hanging pawns to be related.
21. Italian bishop
A White bishop developed to the c4 square or a Black bishop developed to c5. This development is characteristic of the Italian Game, 1.e4 e5 2.Nf3 Nc6 3.Bc4, particularly the Giuoco Piano, 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5, where both players have Italian bishops. Likewise, "Italian" may be used as an adjective denoting an opening where one or both players has an Italian bishop, such as after 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.Bc4, the Italian Four Knights Game.
(from French) "I adjust". A player says "J'adoube" as the international signal that he intends to adjust the position of a piece on the board without being subject to the touched piece rule.