A tax deferral consists of postponing or delaying the payment of taxes on your money and usually on your investments.
Instead of paying taxes now, it is done later. This allows you to use your money and make it profitable until the time comes to pay your taxes.
On the investment side, it has the advantage of allowing you to take better advantage of compound interest and thus increase the return on your investments.
You can check which products make use of this advantage and how each one is taxed here: What taxes you will pay on your investments and the importance of delaying them.