This document discusses code clones in large software systems. It defines code clones as identical or similar segments of code and describes representations of clones as either clone pairs or clone classes. The document notes that while clone detection can find many candidates, not all are useful clones and it is difficult to get a high-level view of cloning at the architecture level. It presents visualization as a way to help understand clones and discusses finding patterns and anti-patterns in clones. The document concludes by questioning the definition of clones and comparing design level similarities to design patterns.