What does the error 'unexpected token readonly expecting abstract or final or class' indicate?

This error indicates that the compiler or interpreter encountered the keyword 'readonly' in a place where it is not allowed. The language (typically C#, Java, or similar) is looking for declarations of abstract classes, final classes, or class definitions, but instead found 'readonly'. This usually occurs when trying to apply the 'readonly' modifier to a member of a class that doesn't inherently possess the necessary declaration type. For example, attempting to make a field readonly within a class that isn't designed as an abstract or final type.