Original: They were the first member of the Electrostar family, which also includes Classes 375, 376, 377 and 378, and is the most numerous type of EMU built in the post-privatisation period of Britain's railways.
Simplified: The Electrostar family also includes Classes 375, 376, 377 and 378, and is the most numerous type of EMU built in the post-privatisation period of Britain's railways.