Interest is when your money earns money. So, if you had £100 in your account, 1.00% AER/Gross p.a. (variable) interest would be £1.00. In other words, you get a bit of extra money, just for keeping money in your account.
Interest is calculated daily and paid monthly.
Annual Equivalent Rate (AER): This is a notional rate used for interest bearing accounts which illustrates the interest rate if paid and compounded each year. It helps you to compare the effective rates of credit interest on different accounts.
Gross Rate: This means the interest rate you are paid before the deduction of basic rate income tax.