An Adapter is a Gang of Four Design Pattern used to allow some client code, already written for the API of class X, to use class Y instead, class Z being implemented to adapt the API of class Y to class X, so that the client code needs no serious modifications.
In WACT, PearRecord, PearRecordSet, AdodbRecord and AdodbRecordSet are Adapters to fit the [MySQLRecord] and [MySQLRecordSet] respectively.
For more information see phpPatterns on the Adapter Pattern