If you click the radio buttons next to those fares the fare class and a list of rules will appear below. From a dummy booking for JNB/LHR I see the following:

- Saver: G class; non-refundable, no changes
- Plus: T class; 25% cancellation fee; $175 change fee
- Classic: S class; 25% cancellation fee; $100 change fee
- Select: K class; Fully flexible, refundable, upgradeable