basic means every month u got the same amount
while allowance, let say petrol allowance, u only got that amount even if ur petrol claim more than that
like telephone allowance, if ur phone bill exceed the amount then they will deduct from ur basic or u pay cash for it
like attendance allowance, if u attend full working days in a month, u will get that amount, if not they will deduct according to ur absences
if performance allowance, if u perform u will get if not u wont^^