What does AER variable interest rate mean?

Variable interest rate means the interest rate you receive on your savings is not fixed and can change. 

With some accounts, you might agree to lock your money away for a certain period of time, guaranteeing that you’ll receive a specific interest rate for the duration; these are known as fixed accounts. With a variable interest rate, the interest you receive fluctuates with the Bank of England base rate (so it can decrease or increase).