Barrett, as an aside, the medical profession may not refer to such things as a rebreather bag (or in fact the item I was referring to is incorrectly named in our paperwork) but I can tell you that three airlines I know of refer to them as such.
Not that we're saying it's correct, it's just the term most cabin crew would know them by. Ambu Bag is probably a brand name for the same thing mentioned before. It's what I know it as, I don't doubt medical personnel would call it something else.