Benoni Defense

The Benoni Defense is a chess opening characterized by the moves:
Black can then sacrifice a pawn with 3...b5 (the Benko Gambit), otherwise 3...e6 is the most common move (although 3...d6 or 3...g6 are also seen, typically transposing to main lines).
The Benoni is very popular among amateurs, and is seen occasionally even at the highest level, with both Fabiano Caruana and Maxime Vachier-Lagrave using it in tournament games in 2019.
Etymology.
"Ben oni" (בֶּן־אוֹנִי) is a Hebrew term meaning "son of my sorrow" (cf. Genesis 35:18) – the name of an 1825 book by Aaron Reinganum about several defenses against the King's Gambit and the Queen's Gambit.
Old Benoni: 1.d4 c5.
The Old Benoni starts with 1.d4 c5. The Old Benoni may transpose to the Czech Benoni, but there are a few independent variations. This form has never attracted serious interest in high-level play, though Alexander Alekhine defeated Efim Bogoljubow with it in one game of their second match, in 1934. The Old Benoni is sometimes called the Blackburne Defense, after Englishman Joseph Henry Blackburne, the first player known to have used it successfully.
Czech Benoni: 1.d4 Nf6 2.c4 c5 3.d5 e5.
In the Czech Benoni, also known as the Hromadka Benoni, after Karel Hromádka, Black plays 1.d4 Nf6 2.c4 c5 3.d5 e5. The Czech Benoni is more than the Modern Benoni, but also more passive. The middlegames arising from this line are characterized by much maneuvering; in most lines, Black will look to break with ...b7–b5 or ...f7–f5 after due preparation, while White may play Nc3–e4–h3–Bd3–Nf3–g4, in order to gain space on the and prevent ...f5. Grandmaster Ben Finegold often plays this line; he notably beat Mamedyarov in this variation.
Modern Benoni: 1.d4 Nf6 2.c4 c5 3.d5 e6.
The Modern Benoni, 1. 2. 3. , is the most common form of Benoni apart from the Benko Gambit. Black's intention is to play ...exd5 and create a , whose advance will be supported by fianchettoed bishop on g7. The combination of these two features differentiates Black's setup from the other Benoni defenses and the King's Indian Defense, although transpositions between these openings are common. The Modern Benoni is classified under the "ECO" codes A60–A79.
Snake Benoni: 4.Nc3 exd5 5.cxd5 Bd6.
The Snake Benoni refers to a variant of the Modern Benoni where the bishop is developed to d6 rather than g7. This opening was invented in 1982 by Rolf Olav Martens, who gave it its name because of the sinuous movement of the bishop—in Martens's original concept, Black follows up with 6...Bc7 and sometimes ...Ba5—and because the Swedish word for "snake", "orm", was an anagram of his initials. Normunds Miezis has been a regular exponent of this variation. Aside from Martens's plan, 6...0-0 intending ...Re8, ...Bf8 and a potential redeployment of the bishop to g7, has also been tried. White appears to retain the advantage against both setups.
"ECO".
The "Encyclopaedia of Chess Openings" ("ECO") has many codes for the Benoni Defense.
Old Benoni Defense:
Benoni Defense:
Fianchetto Variation:
Modern Benoni:
Taimanov Variation:
Four Pawns Attack:
Classical Benoni: