AER means "Annual Equivalent Rate" and is the interest rate you would earn in a 12-month period if you put your money in an account at the beginning and left it there for a full 12 months without adding to it or taking away from it, other than the interest you receive.
The calculation of AER depends on the frequency with which interest is paid.
If the interest is paid once a year, the AER will equal the APR.
If the interest is paid monthly, however, then each month you will earn interest on a little more money (your initial deposit plus any accrued interest to date), so the AER will be higher than the APR.
