Your IBAN is your International Bank Account Number.
This number is used to identify banks across different nations. The first two letters are always the two letter country code of the country it originates from.
An example IBAN for the UK is: GB29 NWBK 6016 1331 9268 19
If you are unsure what your IBAN is, it is most likely available from your online banking institution. You can always call your local branch as well to find out!