6.Bc4 begins the Sozin attack on the classical Sicilian. Black may choose to reply with e6, which is a position easily reached through transposition from the Scheveningen variation as well (6.Bc4,Nc3). However, from the Scheveningen variation white tends to pick other attacks which are more suited to the position, such as the English Attack or the Keres Attack. The Sozin attack is often considered less common and less ambitious than the Richter-Rauzer Attack.
If black does play e6, both players typically develop bishops with white playing Be3 and black responding with Be7. In this position if white castles king side it is called the Fisher-Sozin attack. If white instead moves Qe2 and eventually castles queenside it is called the Velimirovic variation.