Well, CNY is Chinese Yuan, and RMB means Renminbi, they both refer to the same thing - the currency of China.

No difference. They are the same: CNY is short for Chinese Yuan and RMB is short from Renminbi (Chinese money written in Pinyin)

Cool question. I asked my Chinese coworker for the direct translations. Here are the answers for the vault.

Yuan and kuai are general terms for a unit for money. Same as saying dollar, euro, pound.
Renminbi (RMB) and Chinese yuan (CNY) are the official names for the currency. Interchangeable.
Qian (American Eng phonetically- Chie-an) is the general word for any money, any currency.