A more thorough explanation:

A settlement class refers to a group of people who have a common legal position and can efficiently have their claims adjudicated in a single proceeding. This group of people is represented by a claimant's representative and an adversary who propose a contract specifying the payment terms for the class members' claims in exchange for the release of all claims against the adversary.

For example, in the 1980s and 1990s, mass-tort defendants began using settlement classes as a means of foreclosing claims by some unknown number of existing and future claimants. In the case of Amchem Prods., Inc. v. Windsor, 521 U.S. 591, 117 S.Ct. 2231 (1997), the defendant proposed a settlement class for numerous similarly situated people who had been affected by the product in question.

Another example of a settlement class is an opt-out class, which is a plaintiff class certified under Federal Rule of Civil Procedure 23(b)(3), from which class members may choose to exclude themselves if they do not want to be bound by the decisions or settlements reached in the case. Class members may wait until the settlement's terms are announced before choosing to opt out.