Final answer:
A package groups together related classes and interfaces to organize code and prevent naming conflicts in programming languages, like Java, making the correct answer (d).
Step-by-step explanation:
A package in the context of programming, specifically in languages like Java, is a namespace for organizing classes and interfaces. It serves as a container that groups related types together in order to prevent naming conflicts and to control access. Therefore, the correct answer to the question is (d) Classes and interfaces. Packages are typically used to structure the source code in a logical manner, making it easier to maintain and understand. Editing tools and interfaces are not correct as packages don't contain editing tools and do not exclusively contain interfaces either.