What type of reinforcer is money classified as?

Money is classified as a generalized conditioned reinforcer because it acquires its reinforcing properties through association with a wide variety of other reinforcers. Unlike primary reinforcers, which are naturally reinforcing (such as food and water that satisfy biological needs), money itself does not fulfill a basic biological requirement. Instead, its value is derived from its ability to be exchanged for many other things that are reinforcing—like food, clothing, or entertainment.

Since money can help obtain various types of primary and secondary reinforcers, it has a very broad application in reinforcing behaviors across different contexts and settings. This ability to serve as a tradeable medium that can lead to all sorts of desirable outcomes is what fundamentally characterizes it as a generalized conditioned reinforcer.