What is the difference between SSD and flash drives in the latest MacBook Pros?
Usually when Apple says "SSD" they refer to a removable/upgradeable solid-state (flash) storage device. The MBP with Retina Display (and the MacBook Airs) are also using solid-state storage, but they are non-removable.

See also: http://www.pcmag.com/article2/0,2817,2371288,00.asp