A defined benefit is where your retirement benefits are calculated by a predetermined formula, usually based on your average salary over specific years.
Your employer contributes to the amount needed to enable the fund to pay the benefit to you, based on agreed contribution rates and other variables such as inflation.
Accumulation funds are more common and how much you end up with at retirement depends on the money put in by you and your employer, and how it performs.
You bear the risk of your super being lower if financial markets drop. In traditional DBFs, employers bear that risk and have to top up the difference.