A class action suit is a lawsuit brought by a large group of people--a "class"--who all suffered similar or the same injuries from the same event or cause. The most common example is a lawsuit by everyone injured by some defective product or medicine, where you have often hundreds or thousands of persons all injured by the same defect. You also see these in large securities or financial fraud cases, where many people were defrauded or cheated in the same way.There is no such thing as "settlement suit," though the term is sometimes (mis)applied to lawsuits brought in regards to a violation of a previous settlement. For example, say that a company settled or resolved a prior or earlier lawsuit by entering into a settlement (an agreement) providing that they would do (or not do) certain things. If they violate the terms of the agreement, the affected persons (or sometimes the government) can bring a lawsuit to enforce the settlement and seek to punish the person or company violating its suit for the violation.