1.e4 c5, 1.e4 e6, 1.e4 c6, 1.e4 d6, 1.e4 e5, 1.e4 Nf6
In chess the semi-open games are all those variations in which Black does not reply to 1.e2-e4 with 1... e7-e5. The concept semi-open has nothing to do with the types of position which arise, but is simply a historical classification.
In the 19th century1.e4 e5 was by some margin the most popular opening. In the course of the 20th century the semi-open games went on to gain enormously in popularity. The Sicilian (1.e4 c5) has today become the most popular reply to the double step of White’s king’s pawn.
Sicilian: 1.e4 c5
The Sicilian is by far the most popular defence against 1.e4. Black defends against 2.d2-d4. The subsequent asymmetrical centre leads to games which are rich in content and provide chances for both sides. The Sicilian is subdivided into many large sub-systems which have mostly been analysed in depth.
French: 1.e4 e6
In the French Defence Black prepares the counter-thrust in the centre 2.... d7-d5. White usually advances his e-pawn, which restricts Black’s kingside and creates attacking prospects. Black obtains chances of a counter-attack on the white centre and on the queenside.
CaroKann: 1.e4 c6
In the Caro-Kann Defence too Black wants to play 2... d7-d5 immediately. The move 1... c6 looks slightly slow but has the advantage that the bishop on c8 is not shut in. The Caro-Kann is considered a safe defence with good possibilities for development.
Pirc: 1.e4 d6 2.d4 Nf6 3.Nc3 g6
In the Pirc Defence Black at first adopts a passive setup. In the middlegame he will attack the centre usually with ...e5 or ...c5.
Scandinavian: 1.e4 d5
With his counter-thrust Black wants to clear up things in the centre at once. In doing so he accepts the early queen sortie when recapturing on d5. White gets a small but lasting advantage, but Black has a simple plan for development and gets by without too much theoretical knowledge.
Alekhine: 1.e4 Nf6
A double-edged opening which concedes the centre to White. Black provokes the advance of the e-pawn and hopes for counterplay by attacking the advanced white pawns. Not without its venom, but rather rarely seen in top class chess.