A MBA is not a MS or a MA. It is also not a MPH, MHA, or MEd. However, all of these are master's degrees. Does this answer your question?
It, of course, is a master of business administration. A MA is a master of arts and a MS is a master of science. All are different forms of a master's degree and all are legit. None are better than the other and all are respected, depending on what you use them for. Hope that answer is not an insult to your intelligence, it's not intended to be.
To add to the previous comments: First, I just want to clarify that an MBA is neither an MA nor MS. It is a Master's degree, just like an MA or an MS, but it is a specialized degree in business administration, rather than being a Liberal Arts or Sciences degree. There are many of such specialized degrees, some of which have already been listed here. There are also, interestingly enough, MS in Business (Administration) and MA in Business (Administration) and similar degrees. Frankly, why that would be makes no sense to me.
The MBA is a professional degree, and is considered by some to be a "terminal" degree (meaning that it doesn't necessarily prepare one to undertake a PhD). It was intended to be for practitioners, not scholars. This is considered to be an outmoded idea by some. The business-administration MA and MS, in contrast, are not considered terminal degrees nor are they professional degrees. Most MA and MS degrees require a thesis but many MBA degrees do not. There are MA and MS degrees in fields other than business, but an MBA in - for example - English does not exist. These are generalizations, of course.
