Getting cash from Credit Card is expensive. There are multiple type of charges depending on the Bank;
- A fixed Transaction / cash Advance Charge.
- A percentage fee on the amount of withdrawl.
- Interest from the day of withdrawl till the date of payment. [Unlike purchases, there is no grace period for payments]
Getting cash from Debit card is no charge.
Cash Back is the loyalty bonus when you purchase from some stores [can even be wider] essentially involves passing back some of the fees Bank would make back to the customer.
Edit:
On every card swipe of say 100, the merchant gets only 97.5, the rest 2.5 goes as fees, of which the merchant Bank [where the POS/Gateway is connected] gets 0.5, Card Company [Visa/Master/Amex/etc] get 0.5, the Issuing Bank [the one that gave you credit card] gets 1.5. The reason they get large amount is because they give you a average credit of 30 days [at times 10 days at times 50 days depending on when the transaction was done] ...
If the same bank as POS, then on the transaction the Bank makes both legs of fees, ie 2. It is from this fee, they can pass back a small amount say 1 to you.
Again the above is slightly simplified, the fees and distribution varies from Visa to master and from one Merchant Bank to Other, the Cash Back itself is conditional [tied to places where it has POS] or unconditional for limited period to get more customers, or built with other spedning incentives [ie spend minimum of X amount to get cash bank], essentially encouraging spending and not all may be rewarded, or a cap on the total cash back given.