By interest rate we mean the cost of the borrowed money. This money can be borrowed for a mortgage or any other type of loan.
The banks will still ask for an interest rate for the sum that has been granted.
The official interest rate is the rate at which the central banks of individual countries grant loans to ordinary credit institutions by demanding as collateral assets held by the same banks (such as, for example, government bonds).
The official interest rate is controlled directly by the Central Bank and is an important management tool for the liquidity in circulation in the economic system.
Read also What are interest rates?, in order to have a clear view of the situation and clarify any doubts on the matter.