There is no "accepted" definition of the term "obsolete" in the chip collecting hobby. In general it means that the chip is no longer in use. Typically, a chip may be obsolete if the casino closed or if the casino changed the rack. If you want an obsolete chip you have to get one elsewhere, usually from a dealer or another collector. However, there are exceptions. Some chips were never made to be used in the casino, such as commemorative chips, limited editions or souvenir chips that are sold in the casino's gift shop. Since these chips were never in use, how can they be "no longer in use". Sometimes a casino will stop using a chip and then use it again a latter time. Sometimes an obsolete chip from one casino will show up in use at another casino. So there is no exact definition of the term "obsolete".

Chip redemption is an entirely different issue. When you have a casino chip, it is like having money on deposit at a bank. States that regulate gaming are likely to make rules about chip redemption just as they do concerning banks or any other enterprise that is holding your money. Chip redeption rules vary from state to state.