In aspect-oriented software development, cross-cutting concerns are aspects of a program that affect several modules, without the possibility of being encapsulated in any of them. These concerns often cannot be cleanly decomposed from the rest of the system in both the design and implementation, and can result in either scattering (code duplication), tangling (significant dependencies between systems), or both.
For instance, if writing an application for handling medical records, the indexing of such records is a core concern, while logging a history of changes to the record database or user database, or an authentication system, would be cross-cutting concerns since they interact with more parts of the program.