@oristarA,
In its simplist form, a group of injured persons combine to file a lawsuit against a person or corporation, saving legal fees and hundreds or more separate court actions. I believe a class action must be certified as such by a court. That would be a class action. A class settlement would be an agreement reached between parties to avoid legal expenses.
It's worth noting that once a person is part of a designated class, he has little or no influence over the settlement. Also, some companies feel they have been extorted as the cost of defending the action may be more than the cost of a settlement.