In the order of amount of formal schooling required (some of them are very close to each other):
LPN - licensed practical nurse (usually associate degree level?)
RN - Registered nurse
RN, BSN - Registered nurse with a bachelor's degree in nursing (college degree)
CRNA - Nurse anesthetist, ability to practice anesthesia under physician supervision after completing RN, BSN and additional training
PA - Physicians Assistant - special post-college degree resulting in ability to practice supervised medicine
NP - nurse practicioner, a nurse who can practice medicine under physician supervision
MD - doctor of medicine, a doctor who evaluates and treats patients as part of a health care team with the above, and supervises NP's, PA's, etc.
DO - Doctor of osteopathic medicine, historically different from but overall similar to MD's with the exception of additional treatment in physical manipulation.
Unfortunately I don't know what requirements are to license overseas nurses to practice here in the states, but that should give you a good idea of what the abbreviations mean.
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