Sony's FA-CS1M Off-Camera Shoe attaches to an external flash equipped with the multi-interface shoe, and connects it to Sony's wired off-camera eTTL flash control system introduced by Minolta. This wired system provides off-camera eTTL exposure control of flash units in cases where the wireless system can't be used.
The FA-CS1M provides you the 4-pin port that accepts the system's wired connector. Any external flash with the multi-interface shoe that doesn't already have this 4-pin port is compatible. The required 4-pin connector cables FA-CC1AM, FA-CS1AM and FA-EC1AM are available separately.