This may be a silly question, but what is a "cable"? Is this like a telegram or is it just another name for emails? I see here: http://en.wikisource.org/wiki/E

This may be a silly question, but what is a "cable"? Is this like a telegram or is it just another name for emails? I see here: http://en.wikisource.org/wiki/Executive_Order_13526#Part_1 http://en.wikisource.org/wiki/Executive_Order_13526#Part_1 that there's some structure to these documents, but what transport are they being sent by?