royalcrown a word's meaning comes not from it's hard-line definition, but from how it's used by a majority of people. Language is not mathematics. Most people would call Western Digital's system here a 'drive'. They would not be wrong, and neither is Rachel, except in a technical sense. Calling it an 'enclosure' is not only incorrect in a technical sense it is incorrect in the way people speak; to most of us, 'enclosure' would mean something provided that you put things in to, not something that comes already filled.
If you want to nitpick then be right; Western digital calls it a system, and that's what it is - 2 hard drives in an enclosure with software and hardware so it can be used in a 'Raid 0 or 1' configuration. If you want to be right, technically, call it a 'hard drive system'. If you want to communicate correctly, then use the language people understand; most would call this device a 'drive' over an 'enclosure'. Western Digital calls it a 'System'. Since I like to be right technically and say things in a way most would understand, I'd call this thing an external hard drive backup system. Off the cuff, though, I'd call it a 'drive', certainly not an 'enclosure'.